Here’s a common challenge when tuning a race car from trackside – you want a particular improvement, but you are limited to a specific choice of possible changes or adjustments. It’s not unusual for one change have several possible effects.
For example, let’s say the car is unstable on corner entry, due to some oversteer on initial turn-in. Let’s say you’ve decided to try to cure this by adding some anti-dive to the front suspension geometry.
In an ideal world, your car will have finely adjustable heights at both the fore and aft inboard pickup points of the upper and lower A-frames. You will whip out the laptop, make a quick run of your kinematics software, and away you go.
But, it’s the real world. Let’s say the only trackside adjustment available is the height of the inboard pickup at the rear of the upper A-frame.
See where this leads – adjusting that inner pickup point will not only change the anti-dive, it will also change the roll center height, the camber gain, and the caster gain. Will those changes work for you or against you?
In a fit of indecision, you decide to abandon the notion of adding anti-dive, and just make a shock adjustment to prop up the front end with a little low speed bump damping. Uh oh, trouble again. More low speed damping could indeed prop up the front, but then again, it could possibly make the entry oversteer even worse by sharpening the turn-in.
Things can get uglier. A stiffer front anti-roll bar, raising the front roll center, stiffer front springs, less front downforce are all changes with more than one possible outcome.
So, here’s the question: Who wins?
First, you’ve got to identify all the possible effects of the change you’re considering. Then, you’ve got to identify the magnitude of difference you are making on each of those effects. After that, you’ve got to decide how powerful each effect is on handling. Finally, and perhaps most importantly, you’ve got to assess whether the effects all work in the direction you want to go, or if some effects work against your desired result, or even in some wholly new direction.
If all the possible effects work in the same tuning direction, you have a winner! The probability of getting the desired result is pretty good, unless you commit the error of making too big a change and “going over center”.
The fun starts when some effects work against others. Using the anti-dive example, let’s say the only adjustment available to us is the height of the forward inner pickup point of the upper A-frame. If you raise it to increase anti-dive, you also lower the front roll center, possibly increasing front grip and working against your desired result. Who wins?
The danger…
As you stand there on pit lane, with a vacant look on your face, considering the possibilities, the driver and mechanics are growing increasingly impatient.
There are two ways to avoid this happening. One way is analysis. Work through the changes possible on your car ahead of time and consider your options. Hand calculations, vehicle dynamics analysis, and simulation runs can all be helpful. The other way is to scan various changes on your car and learn how it reacts, preferably doing this on an open test day. Both will help with a quick “gut call” on pit lane in the middle of a busy practice session on a race weekend.
Tuesday, August 30, 2011
Monday, May 16, 2011
Race Strategy - Indy 500 compared to Rolex GT
The May 2011 issue of Racecar Engineering recently arrived in the mail. The cover promised that Andy Brown, Target Ganassi engineer, would reveal the secrets of Indy 500 race-winning strategy calls. I opened it right up and read the article with interest, having made race strategy calls in ALMS and Grand Am for the past 11 seasons.
Now, I’m not normally one for comparisons – my dog is meaner than yours, my car is faster than yours, and so on. And I don’t know if Andy told it all, or just the parts that he thought would be obvious enough that his competitors would have already figured them out. Also, I don’t have recent experience with the Indycar rules and race control procedures, so I’m assuming everything relevant from them is factored into Andy’s strategy calls.
But, I gotta tell you, it sure looks equally, if not more, challenging to call a GT class car in a Grand Am Rolex race than it does to call the Indy 500. Here’s why:
Number of sets of tires
Indy 500 – Limited number of tire sets
Rolex GT – Limited number of tire sets
Comparison – Neither series seriously cramps your style on race day, unless things get weird. Same for both.
Tire performance
Indy 500 – Tires wear out in slightly more than one stint. No performance falloff over the stint.
Rolex GT – Tires don’t wear out. Performance falls off considerably over the stint.
Comparison – The end result is similar.
There is a “drop dead” point in a fuel stint for either series, beyond which you must change tires. Rule of thumb applies for a relatively easy call during the race.
Race length
Indy 500 – 200 laps, and that’s that.
You know exactly how many laps remain, but the timing, number, and duration of caution periods will affect your strategy.
Rolex GT – All races by time, not by number of laps
You can calculate how many laps remain, IF the remainder of the race stays green. If there are yellows, the number of laps remaining reduces, since a pace car laps takes more time than a green race lap.
Comparison – Rolex is tougher
Yellow flag laps save fuel AND reduce the number of laps remaining. So, you have a moving target. If you wait until you are clearly in the window to the end of the race before pitting, you will likely give up track position to those who gambled and pitted prior to the window, counting on being saved by a yellow or two before the finish. But, how early is too early? And what if there isn’t a yellow to save you, and now you have to stop for a splash to make it to the end, giving up track position? No easy answers…
Green flag pit stops
Indy 500 – You lose a lap
So, it’s fairly straightforward. You try to avoid intentionally forcing yourself to pit under green.
Rolex GT – You may lose a lap. Then again, you may not.
It depends on how long a green flag lap takes, which in turn is depends on both track length and average speed. It also depends on how long the pit lane is and how fast the past car goes. And, it depends on whether you need a full fuel fill or partial, and whether you must change tires or not. So, it may be a sin to stop under green, or it may be an advantage, depending on the situation.
Comparison – Rolex is tougher
Any time you can set a “rule of thumb”, that’s one less thing to worry about during the race. And, even at little bullrings like Barber, there’s no sure rule of thumb for Rolex green flag stops.
Pace car waveby
Indy 500 – Leader restarts first. Cars between leader and pace car waved by. Pits closed.
You can forego a pit stop if circumstances lead you to expect a waveby. Useful to get back on the lead lap, if you don't lose it again with a green flag stop shortly afterward.
Rolex GT – DP leader restarts first. Cars between pace car and leader waved by. Pits open.
Here’s a critical distinction. The “GT” leader can indeed take the waveby, if in front of the DP leader, thereby gaining nearly a full lap on any GT cars that do not take the waveby. ALMS used to do this too, but they changed their rules a couple of seasons ago to avoid creating this situation. And, the pits are open, so you can also make a pit stop, if you think you can beat the pace car around, then pit and get out before the pack arrives. The waveby is on the final lap of caution, though, and there won’t be time to pit AND catch the field. Not to mention the increased risk if something goes wrong during the pit stop. High stakes, high rewards, quick decisions
Comparison – Rolex GT is tougher
Tougher than Indy, and tougher than DP, too. Whenever the race leader can get a waveby, the stakes are high.
Rain
Indy 500 - Park it
Rolex GT - Keep going
Comparison - You've got to decide when to switch to wet tires and when to switch to back to dry tires, and whether to do this under green or wait for the nearly inevitable caution. Then, there's the question of how thoroughly do you convert the setup to wet specs, and whether to make any of these changes during a pit stop. And finally, there's a lot of dependence on driver comments.
Reading what I've written, I'm afraid you'd conclude that I'm saying the lot of the Rolex GT race strategist is tougher than that of the Indy 500 strategist. I seriously doubt that is true, and that's not my intent, as I said at the start. They are competing against teams with deep specialized experience in a unique event. There is little margin for error, or even for good, but not optimum, strategy calls. Meanwhile, endurance road racing has a certain amount of fuzziness that can compensate for these same good, but not optimum calls. Apples and oranges...
Still, I think it's pretty clear that calling strategy for a GT car in a garden-variety Rolex race is at least as challenging a calling the 500. And that was a bit of a surprise to me when I read Andy's article.
Special thanks to Andy Brown for opening up on this subject, one that most race engineers, team managers, and other race strategists would rather not discuss.
Now, I’m not normally one for comparisons – my dog is meaner than yours, my car is faster than yours, and so on. And I don’t know if Andy told it all, or just the parts that he thought would be obvious enough that his competitors would have already figured them out. Also, I don’t have recent experience with the Indycar rules and race control procedures, so I’m assuming everything relevant from them is factored into Andy’s strategy calls.
But, I gotta tell you, it sure looks equally, if not more, challenging to call a GT class car in a Grand Am Rolex race than it does to call the Indy 500. Here’s why:
Number of sets of tires
Indy 500 – Limited number of tire sets
Rolex GT – Limited number of tire sets
Comparison – Neither series seriously cramps your style on race day, unless things get weird. Same for both.
Tire performance
Indy 500 – Tires wear out in slightly more than one stint. No performance falloff over the stint.
Rolex GT – Tires don’t wear out. Performance falls off considerably over the stint.
Comparison – The end result is similar.
There is a “drop dead” point in a fuel stint for either series, beyond which you must change tires. Rule of thumb applies for a relatively easy call during the race.
Race length
Indy 500 – 200 laps, and that’s that.
You know exactly how many laps remain, but the timing, number, and duration of caution periods will affect your strategy.
Rolex GT – All races by time, not by number of laps
You can calculate how many laps remain, IF the remainder of the race stays green. If there are yellows, the number of laps remaining reduces, since a pace car laps takes more time than a green race lap.
Comparison – Rolex is tougher
Yellow flag laps save fuel AND reduce the number of laps remaining. So, you have a moving target. If you wait until you are clearly in the window to the end of the race before pitting, you will likely give up track position to those who gambled and pitted prior to the window, counting on being saved by a yellow or two before the finish. But, how early is too early? And what if there isn’t a yellow to save you, and now you have to stop for a splash to make it to the end, giving up track position? No easy answers…
Green flag pit stops
Indy 500 – You lose a lap
So, it’s fairly straightforward. You try to avoid intentionally forcing yourself to pit under green.
Rolex GT – You may lose a lap. Then again, you may not.
It depends on how long a green flag lap takes, which in turn is depends on both track length and average speed. It also depends on how long the pit lane is and how fast the past car goes. And, it depends on whether you need a full fuel fill or partial, and whether you must change tires or not. So, it may be a sin to stop under green, or it may be an advantage, depending on the situation.
Comparison – Rolex is tougher
Any time you can set a “rule of thumb”, that’s one less thing to worry about during the race. And, even at little bullrings like Barber, there’s no sure rule of thumb for Rolex green flag stops.
Pace car waveby
Indy 500 – Leader restarts first. Cars between leader and pace car waved by. Pits closed.
You can forego a pit stop if circumstances lead you to expect a waveby. Useful to get back on the lead lap, if you don't lose it again with a green flag stop shortly afterward.
Rolex GT – DP leader restarts first. Cars between pace car and leader waved by. Pits open.
Here’s a critical distinction. The “GT” leader can indeed take the waveby, if in front of the DP leader, thereby gaining nearly a full lap on any GT cars that do not take the waveby. ALMS used to do this too, but they changed their rules a couple of seasons ago to avoid creating this situation. And, the pits are open, so you can also make a pit stop, if you think you can beat the pace car around, then pit and get out before the pack arrives. The waveby is on the final lap of caution, though, and there won’t be time to pit AND catch the field. Not to mention the increased risk if something goes wrong during the pit stop. High stakes, high rewards, quick decisions
Comparison – Rolex GT is tougher
Tougher than Indy, and tougher than DP, too. Whenever the race leader can get a waveby, the stakes are high.
Rain
Indy 500 - Park it
Rolex GT - Keep going
Comparison - You've got to decide when to switch to wet tires and when to switch to back to dry tires, and whether to do this under green or wait for the nearly inevitable caution. Then, there's the question of how thoroughly do you convert the setup to wet specs, and whether to make any of these changes during a pit stop. And finally, there's a lot of dependence on driver comments.
Reading what I've written, I'm afraid you'd conclude that I'm saying the lot of the Rolex GT race strategist is tougher than that of the Indy 500 strategist. I seriously doubt that is true, and that's not my intent, as I said at the start. They are competing against teams with deep specialized experience in a unique event. There is little margin for error, or even for good, but not optimum, strategy calls. Meanwhile, endurance road racing has a certain amount of fuzziness that can compensate for these same good, but not optimum calls. Apples and oranges...
Still, I think it's pretty clear that calling strategy for a GT car in a garden-variety Rolex race is at least as challenging a calling the 500. And that was a bit of a surprise to me when I read Andy's article.
Special thanks to Andy Brown for opening up on this subject, one that most race engineers, team managers, and other race strategists would rather not discuss.
Wednesday, March 2, 2011
Setup Questions from Readers
In response to a recent reader request, this post will kick off a more interactive way to blog.
The reader asked, "Would you mind answering some setup questions on the blog?"
You bet. Here we go. Send your questions in the comments to this post.
Let's do it this way:
1-Keep the questions short, punchy, and focused. It's difficult, if not impossible, to reply to something as broad as "How do I get rid of mid-corner understeer?" in a short answer.
2-If there are a lot of questions, I may have to pick and choose which ones to answer. If your question doesn't show up in the blog comments, it's either been delayed or set aside.
3-In this initial thread, why don't we limit questions to setup? Maybe we'll start another thread or two later for other topics, like "life as a race engineer", race strategy, organization and planning, etc. In other words, other topics in the scope of the blog.
4-I'm going to reserve the option to wrap up the thread, for later resurrection, if needed. My upcoming schedule is pretty busy and I'd rather avoid leaving a bunch of folks hanging.
The reader asked, "Would you mind answering some setup questions on the blog?"
You bet. Here we go. Send your questions in the comments to this post.
Let's do it this way:
1-Keep the questions short, punchy, and focused. It's difficult, if not impossible, to reply to something as broad as "How do I get rid of mid-corner understeer?" in a short answer.
2-If there are a lot of questions, I may have to pick and choose which ones to answer. If your question doesn't show up in the blog comments, it's either been delayed or set aside.
3-In this initial thread, why don't we limit questions to setup? Maybe we'll start another thread or two later for other topics, like "life as a race engineer", race strategy, organization and planning, etc. In other words, other topics in the scope of the blog.
4-I'm going to reserve the option to wrap up the thread, for later resurrection, if needed. My upcoming schedule is pretty busy and I'd rather avoid leaving a bunch of folks hanging.
Sunday, February 6, 2011
The Daytona 24 Hour Race
The 24 Hour race at Daytona is, for crews, quite possibly the toughest road race in the world. Some thoughts:
Darkness
It’s dark for just about twelve hours, much longer than at Le Mans. Le Mans is dark for only about half as long, between its June date and its northern latitude. And the “new” start time for Daytona of 3:30 PM, instituted just a few years ago (for TV?) insures that it will get dark very soon after the start of the race. Of course, the darkness isn’t as big a challenge for the drivers as it might initially appear to be. The course is fairly well lit, not at all like blackness of Le Mans, Sebring, or the 25 hour race at Thunderhill. For the crews, the effect of the long darkness is this: You know you are going to have to miss a night’s sleep. So, you want the night to be over, so you can at least stand a better chance of staying alert in the light of the second day. But, the night drags on and on, and so do you.
The early visit to the garage
The worst thing for any team member is, sometime in the first half of the race, getting that radio call from the driver that the car has been involved in an incident or isn’t running right. If the solution takes 30 minutes in the garage, you are totally out of contention. And yet, there’s still the remainder of the night’s sleep to miss, 10 more pit stops to accomplish successfully, and the reward of loading a trailer when it’s all over.
It’s the first race
Preparing the car is a lot of work. Everything on it has to be touched, freshened, made ready for a long trouble-free run. As soon as the race is over, there is even more work ahead to restore the car to top condition for the next race.
It’s a 24 hour sprint
Yes, I know the TV commentators are fond of pointing this out every year. Yes, they are right. The significance of this isn’t really about the cars, though. The cars, both DP and GT, are fully capable of being run hard for 24 straight hours, without any babying. The real significance is on the crew. The engineers have to be on their game for race strategy and tactics. The over-the-wall guys have to execute 24 or more fast and flawless pit stops.
Smart phones and other connectivity
Having an Android, iPhone, iPad, or Blackberry on the timing stand has become essential. The number one reason is to monitor weather radar. That's such a biggie! A very close number two is NEVER losing touch with your drivers. It used to sometimes be fun to locate the driver who was due for the next stint. Beyond that - tweets, Facebook status updates, and texting help keep everyone in the loop. If done correctly (and not obsessively), they don't get in the way of running the race. This year, our PR guy was updating the website every hour or two, direct from the timing stand, via his PC's wireless card. If done wrong, it's just tech obsession. If done right, everything is lifted a notch.
Brakes
Grand-Am doesn’t allow carbon brakes, which can comfortably last 24 hours. With the “sprint” nature of the race, teams may choose to run aggressive pad compounds, in search of improved braking performance. For an engineer working on a unfamiliar car, or for a new team, or for a team running its first 24 hour on a new brake pad compound, there is always a bit of uncertainty. Did we get enough practice running to forecast pad and rotor life accurately? Have we correctly judged the tradeoff of braking performance against brake life? Will we get a conveniently timed caution flag to allow changing pads, or will we be stuck with changing them in a green flag pit stop?
Is it cold enough for you?
The overnight low is frequently in the mid 40s, and can be colder. That doesn’t sound so grueling, does it? Not so. Being outdoors, and yet largely immobile, for eight or ten hours straight in mid 40s, with no warmth from the sun, can be chilling and draining, both physically and mentally. There’s no secret, but having a tent with enclosed sides, staying hydrated and well fed, and wearing every stitch of warm clothing that you own can all help.
The payoff
Win or lose, there’s a fine sense of accomplishment that comes with seeing the checker. That’s what keeps us all coming back.
See you there next year!
Darkness
It’s dark for just about twelve hours, much longer than at Le Mans. Le Mans is dark for only about half as long, between its June date and its northern latitude. And the “new” start time for Daytona of 3:30 PM, instituted just a few years ago (for TV?) insures that it will get dark very soon after the start of the race. Of course, the darkness isn’t as big a challenge for the drivers as it might initially appear to be. The course is fairly well lit, not at all like blackness of Le Mans, Sebring, or the 25 hour race at Thunderhill. For the crews, the effect of the long darkness is this: You know you are going to have to miss a night’s sleep. So, you want the night to be over, so you can at least stand a better chance of staying alert in the light of the second day. But, the night drags on and on, and so do you.
The early visit to the garage
The worst thing for any team member is, sometime in the first half of the race, getting that radio call from the driver that the car has been involved in an incident or isn’t running right. If the solution takes 30 minutes in the garage, you are totally out of contention. And yet, there’s still the remainder of the night’s sleep to miss, 10 more pit stops to accomplish successfully, and the reward of loading a trailer when it’s all over.
It’s the first race
Preparing the car is a lot of work. Everything on it has to be touched, freshened, made ready for a long trouble-free run. As soon as the race is over, there is even more work ahead to restore the car to top condition for the next race.
It’s a 24 hour sprint
Yes, I know the TV commentators are fond of pointing this out every year. Yes, they are right. The significance of this isn’t really about the cars, though. The cars, both DP and GT, are fully capable of being run hard for 24 straight hours, without any babying. The real significance is on the crew. The engineers have to be on their game for race strategy and tactics. The over-the-wall guys have to execute 24 or more fast and flawless pit stops.
Smart phones and other connectivity
Having an Android, iPhone, iPad, or Blackberry on the timing stand has become essential. The number one reason is to monitor weather radar. That's such a biggie! A very close number two is NEVER losing touch with your drivers. It used to sometimes be fun to locate the driver who was due for the next stint. Beyond that - tweets, Facebook status updates, and texting help keep everyone in the loop. If done correctly (and not obsessively), they don't get in the way of running the race. This year, our PR guy was updating the website every hour or two, direct from the timing stand, via his PC's wireless card. If done wrong, it's just tech obsession. If done right, everything is lifted a notch.
Brakes
Grand-Am doesn’t allow carbon brakes, which can comfortably last 24 hours. With the “sprint” nature of the race, teams may choose to run aggressive pad compounds, in search of improved braking performance. For an engineer working on a unfamiliar car, or for a new team, or for a team running its first 24 hour on a new brake pad compound, there is always a bit of uncertainty. Did we get enough practice running to forecast pad and rotor life accurately? Have we correctly judged the tradeoff of braking performance against brake life? Will we get a conveniently timed caution flag to allow changing pads, or will we be stuck with changing them in a green flag pit stop?
Is it cold enough for you?
The overnight low is frequently in the mid 40s, and can be colder. That doesn’t sound so grueling, does it? Not so. Being outdoors, and yet largely immobile, for eight or ten hours straight in mid 40s, with no warmth from the sun, can be chilling and draining, both physically and mentally. There’s no secret, but having a tent with enclosed sides, staying hydrated and well fed, and wearing every stitch of warm clothing that you own can all help.
The payoff
Win or lose, there’s a fine sense of accomplishment that comes with seeing the checker. That’s what keeps us all coming back.
See you there next year!
Tuesday, September 7, 2010
Rain Setups
First, sincere apologies to faithful readers for the long, long dry spell in new blog posts. I’ve been busy with two racing programs. That’s the reason, but it’s no excuse. Oh, well.
If you followed the 2010 ALMS race weekend at Lime Rock, then the topic of this blog will come as no surprise at all. Let’s end the dry spell in blog posts by talking about rain.
I’ll be the first to tell you that I am never totally comfortable with rain setups, despite having run in the rain quite a bit and even having engineered a major series race win in the rain. Rain setups are always a conundrum. First, you don’t get a lot of opportunities to develop your rain setup. Then, there’s the really big question of how far do you take the rain setup. Then, there’s the other really big question of how skilled and comfortable your driver is on a wet track. Compared to those, the technical issues of the rain setup are almost “cut and dry”, to make a weak pun. Contrary to what the advice columns say, I’ll tackle the easy part first.
For starters, let’s assume we have a properly wet track (at least light rooster tails), with rain still falling at a steady enough rate to keep the track from drying. It’s been raining for a while, and there isn’t much heat left in the pavement. We don’t anticipate that it will quit raining during the session.
Let’s start with a small handful of basic principals. We need grip. The brake bias needs to be shifted to the rear. We absolutely cannot tolerate understeer. Let me say that one more time. We absolutely cannot tolerate understeer.
Chasing grip first…
First, we need all the downforce we can produce. Wing(s) to the maximum, more rake, add on all the gadgets, do it all. Drag be damned. That much, I know for sure. It’s essential that we remain respectful of the car’s fundamental aero characteristics. Pitch and ride height sensitivity will affect decisions to adjust rake, as well as spring or bump rubber rate decisions. I believe that as you add total downforce, you need to try to keep the aero balance as far forward as possible. All in the interest of avoiding understeer.
In pursuit of grip, it’s tempting to dramatically open the bump and rebound bleeds in the shocks. On the other hand, we need to remain respectful of the car’s needs for aero platform control, which may or may not change in the rain. We also have to remember that the bumps, curbs, and other surface irregularities in the track will not go away just because they get wet. So, how much bleed is enough? It depends.
In race series where the rules allow driver-adjustable anti-roll bars, it’s easy to soften the bars for some grip. Perhaps equally important, it’s easy to reverse the adjustment. In other series, it becomes more of a judgment call whether to soften the bars, and if so, how much.
So that’s it for the easy changes. Now, if it’s really clear that the rain will continue, and at a track-soaking pace, we can also consider softening springs and reducing negative camber. Again, we need to be cognizant of platform control, if we choose to soften springs. It’s much safer to soften dramatically on a low-dowforce car than on a high-downforce one. Meanwhile, the camber change can be quite helpful, presuming the weather has the courtesy to stay properly wet. If not, you’re in trouble, aren’t you?
Finally, let’s have a look at the rain tires themselves. How fresh are they? If they’ve been previously run on a drying track, they will have worn away the chiseled edges that are so essential to cutting through the water to the track. If it’s really wet, fresh rains always help.
Now, a brief word about brake bias…
Braking Gs in the rain won’t be as high as in the dry, so we won’t have as much forward weight transfer. Lacking that, we’ll need less front brake bias. It’s pretty easy to make a rough calculation of the needed change. The whole process is almost painless if you have driver-adjustable bias and brake pressure sensors wired into onboard math in the data logger and displayed on the dash. A word to the wise – brake bias adjusters can be cranky little pieces of crap, and the time to debug them is not when the rain starts falling.
OK, so let’s talk about understeer…
Understeer in the rain is more than just an inconvenience. It’s an opportunity to arrive at a corner and plow straight off into the muddy grass, gravel, wall, or whatever other dramatic and damaging fate awaits the car. Not good, and it won’t endear you to either the driver or the mechanics.
Let’s remember that our dry-track handling balance assumes a lot of weight transfer to the front in braking, helping corner entry. Then, on exit, the rear lateral grip is reduced with an aggressive application of power. Neither condition is there for us in the wet. It will be necessary to shift the handling balance in the oversteer direction. It’s not as simple as aggressively softening the front springs and bar, because that might lose aero or roll platform control in a way we won’t like. You should work within the tuning options you’ve proven for your car in the dry.
The oft-mentioned option to disconnect both the front and rear anti-roll bars can, in the right circumstances, be a good move for preventing understeer. The wheel rate of the front bar is almost always higher than the rear. Nuff said.
Here are two serious “gotchas” related to cooling…
First, be careful of your engine temperatures. Some ECU calibrations may default into “cold-start” mode if temperatures drop too much.
And, some brake materials don’t take kindly at all to getting wet or getting too cool.
Everyone wants to just lay a strip or two of duct tape over the radiator opening or the brake ducts. Step back for a minute and think about how well duct tape will stick to a wet, dirty, oily surface, and you will see why I strongly prefer sheet aluminum blanking plates held in place by Camlocs.
Now, let’s talk drivers for a minute…
Some are really good in the rain, some are OK, and some are, well, not OK. I hope yours is in the first group. If so, you’ll look pretty good, no matter how well the car works. I once had a special case of a driver who was good in the rain, but didn’t care for losing any of his cherished platform support to softer springs, bars, or shocks. We just turned up the wing, reset the brake bias, bolted on the rains, and went off to win the race. As always, tune to the driver’s comments.
So, here’s the ugly question…
How far do you go with “messing up” your nice dry setup for the rain?
Here are some of the questions we’ll need to consider:
Will the rain let up soon, or get worse?
Is it real rain, or just a shower?
How much of the track is wet?
What can we learn from radar and the sky?
When will the track be wet enough to need rains, or dry enough to take them off?
How much heat remains in the track surface?
If this is a practice session, do we expect to qualify or race in the rain?
Do we even go out on the track?
All questions are for another day. Hopefully soon. See you later.
If you followed the 2010 ALMS race weekend at Lime Rock, then the topic of this blog will come as no surprise at all. Let’s end the dry spell in blog posts by talking about rain.
I’ll be the first to tell you that I am never totally comfortable with rain setups, despite having run in the rain quite a bit and even having engineered a major series race win in the rain. Rain setups are always a conundrum. First, you don’t get a lot of opportunities to develop your rain setup. Then, there’s the really big question of how far do you take the rain setup. Then, there’s the other really big question of how skilled and comfortable your driver is on a wet track. Compared to those, the technical issues of the rain setup are almost “cut and dry”, to make a weak pun. Contrary to what the advice columns say, I’ll tackle the easy part first.
For starters, let’s assume we have a properly wet track (at least light rooster tails), with rain still falling at a steady enough rate to keep the track from drying. It’s been raining for a while, and there isn’t much heat left in the pavement. We don’t anticipate that it will quit raining during the session.
Let’s start with a small handful of basic principals. We need grip. The brake bias needs to be shifted to the rear. We absolutely cannot tolerate understeer. Let me say that one more time. We absolutely cannot tolerate understeer.
Chasing grip first…
First, we need all the downforce we can produce. Wing(s) to the maximum, more rake, add on all the gadgets, do it all. Drag be damned. That much, I know for sure. It’s essential that we remain respectful of the car’s fundamental aero characteristics. Pitch and ride height sensitivity will affect decisions to adjust rake, as well as spring or bump rubber rate decisions. I believe that as you add total downforce, you need to try to keep the aero balance as far forward as possible. All in the interest of avoiding understeer.
In pursuit of grip, it’s tempting to dramatically open the bump and rebound bleeds in the shocks. On the other hand, we need to remain respectful of the car’s needs for aero platform control, which may or may not change in the rain. We also have to remember that the bumps, curbs, and other surface irregularities in the track will not go away just because they get wet. So, how much bleed is enough? It depends.
In race series where the rules allow driver-adjustable anti-roll bars, it’s easy to soften the bars for some grip. Perhaps equally important, it’s easy to reverse the adjustment. In other series, it becomes more of a judgment call whether to soften the bars, and if so, how much.
So that’s it for the easy changes. Now, if it’s really clear that the rain will continue, and at a track-soaking pace, we can also consider softening springs and reducing negative camber. Again, we need to be cognizant of platform control, if we choose to soften springs. It’s much safer to soften dramatically on a low-dowforce car than on a high-downforce one. Meanwhile, the camber change can be quite helpful, presuming the weather has the courtesy to stay properly wet. If not, you’re in trouble, aren’t you?
Finally, let’s have a look at the rain tires themselves. How fresh are they? If they’ve been previously run on a drying track, they will have worn away the chiseled edges that are so essential to cutting through the water to the track. If it’s really wet, fresh rains always help.
Now, a brief word about brake bias…
Braking Gs in the rain won’t be as high as in the dry, so we won’t have as much forward weight transfer. Lacking that, we’ll need less front brake bias. It’s pretty easy to make a rough calculation of the needed change. The whole process is almost painless if you have driver-adjustable bias and brake pressure sensors wired into onboard math in the data logger and displayed on the dash. A word to the wise – brake bias adjusters can be cranky little pieces of crap, and the time to debug them is not when the rain starts falling.
OK, so let’s talk about understeer…
Understeer in the rain is more than just an inconvenience. It’s an opportunity to arrive at a corner and plow straight off into the muddy grass, gravel, wall, or whatever other dramatic and damaging fate awaits the car. Not good, and it won’t endear you to either the driver or the mechanics.
Let’s remember that our dry-track handling balance assumes a lot of weight transfer to the front in braking, helping corner entry. Then, on exit, the rear lateral grip is reduced with an aggressive application of power. Neither condition is there for us in the wet. It will be necessary to shift the handling balance in the oversteer direction. It’s not as simple as aggressively softening the front springs and bar, because that might lose aero or roll platform control in a way we won’t like. You should work within the tuning options you’ve proven for your car in the dry.
The oft-mentioned option to disconnect both the front and rear anti-roll bars can, in the right circumstances, be a good move for preventing understeer. The wheel rate of the front bar is almost always higher than the rear. Nuff said.
Here are two serious “gotchas” related to cooling…
First, be careful of your engine temperatures. Some ECU calibrations may default into “cold-start” mode if temperatures drop too much.
And, some brake materials don’t take kindly at all to getting wet or getting too cool.
Everyone wants to just lay a strip or two of duct tape over the radiator opening or the brake ducts. Step back for a minute and think about how well duct tape will stick to a wet, dirty, oily surface, and you will see why I strongly prefer sheet aluminum blanking plates held in place by Camlocs.
Now, let’s talk drivers for a minute…
Some are really good in the rain, some are OK, and some are, well, not OK. I hope yours is in the first group. If so, you’ll look pretty good, no matter how well the car works. I once had a special case of a driver who was good in the rain, but didn’t care for losing any of his cherished platform support to softer springs, bars, or shocks. We just turned up the wing, reset the brake bias, bolted on the rains, and went off to win the race. As always, tune to the driver’s comments.
So, here’s the ugly question…
How far do you go with “messing up” your nice dry setup for the rain?
Here are some of the questions we’ll need to consider:
Will the rain let up soon, or get worse?
Is it real rain, or just a shower?
How much of the track is wet?
What can we learn from radar and the sky?
When will the track be wet enough to need rains, or dry enough to take them off?
How much heat remains in the track surface?
If this is a practice session, do we expect to qualify or race in the rain?
Do we even go out on the track?
All questions are for another day. Hopefully soon. See you later.
Wednesday, February 17, 2010
Finding the Setup, Part 2
Have a look at this Wikipedia entry. While not written specifically about racing, it relates directly to Jeff's "secondary effects".
http://en.wikipedia.org/wiki/Law_of_Unintended_Consequences
In response to a request on the FSAE forum, Jeff has kindly taken the time to make a PDF of his setup change spreadsheet. Note that all the second page shows the selections for the pull-downs (not seen) that are used to fill in the individual setup changes on the sheet.
Jeff Braun Setup Change Database PDF
http://en.wikipedia.org/wiki/Law_of_Unintended_Consequences
In response to a request on the FSAE forum, Jeff has kindly taken the time to make a PDF of his setup change spreadsheet. Note that all the second page shows the selections for the pull-downs (not seen) that are used to fill in the individual setup changes on the sheet.
Jeff Braun Setup Change Database PDF
Saturday, February 13, 2010
Finding the Setup
Here's another guest post, this time from Jeff Braun. Jeff's a successful working race engineer, concentrating these days on endurance sports car racing, but with a broad background in many racing series.
He also has the dubious distinction of being the only race engineer who actually drove against me. It was a while ago... If I recall, I beat him then, but he's paid it back as an engineer, more than once.
Since we're friends, I'll indulge him for scooping me on material that was to have been included in the "Philosophy" series. But, there's much more than that in his post. I'm sure you'll find it thought-provoking.
The Setup – How to get it right
Apart from money, a good setup may be the most sought after thing in racing.
One thing before we talk about how to get the setup right. Who is ultimately responsible for the setup on the car? The driver! Not the engineers, not the team manager, not the chief mechanic, or anyone else except the driver. I hate it when people say “the engineer really has that car set up well.” It has little to do with the engineer. I have yet to see an engineer put a setup on a car, install a new driver, never change the setup, and win everything in sight. It never happens. The driver guides the setup process, he directs the engineers in the areas that need improvement, he is in charge of the car, and he has to get it to his liking to be fast. The engineer only interprets what the driver tells him and comes up with suggestions on what changes could help the problems the driver has identified as the main thing preventing him from going quicker. The engineer has the technical resources to come up with the best change to get the desired results, but he can’t identify and prioritize the areas that need improving without a technically good driver to point him in the right direction.
The magic setup – No numbers
Getting the setup right is not about cambers, toe, springs, and all the technical numbers. It is about the approach you take and the procedures you use to get there. So, I am not going to tell you the perfect springs to run at Laguna, or what wing setting works best at Montreal. Why? Because, it all depends on way too many things. I just plain don’t know the answer. What I am sure of is that, if you follow the things below, you will be ahead of the game in finding the springs or wing settings for your driver, your car, and the track on the weekend you are racing.
Best way to a great setup – Don’t change anything!
So, you spend hours with your driver and the data in the shop designing the starting setup for the weekend. You have experience with the car and kind of know the type of track you are going to, but have never been there before. You have it nailed, you think. You unload and head out for the first session. Four laps later, the driver is in the pits looking for a change. You jump in and start changing things; you want it to be better for him.
After the session you make more changes, maybe three or four, because he was 1 second off the pace. Next session the car is doing different things than before. Oh no, the changes were in the wrong direction. You remove the three changes and go the other way with four more. Now it’s better, but now a there is a different problem.
The data looks confusing, the driver is confused, but time is running out now, and you are still 0.8 seconds off. Something must be way different about this track than you thought. You decide you may have to rethink the entire setup, or that you may not really understand the car like you thought.
The next session you are better. The times are closer to fast guys and the driver just needs a few small changes. The changes help and the panic subsides some. But, you still need three tenths.
Now, it’s qualifying. The changes helped, and you’re now two tenths off the pole and on the second row. So, let’s look at the qualifying setup. It is exactly how we unloaded! We went in a big circle.
I see this all the time, at all levels of motorsport. I don’t know of any race engineers who get paid by the change. Slow down. Let the driver learn the track, and then figure out what he needs. The track will clean up and get some rubber down. Have confidence in your starting setup. Don’t be in a hurry to change it all around right away. Talk with your driver and write out a testing plan listing each session and what you hope to get done. This will only be a guide for the weekend, but it allows you to plan the sessions as you wish they would go.
A driver’s feed back is junk for the first session, anyway. He is getting a feel for the track, the grip level, and the car. Use that session to set the ride height (as the best engineer/driver I have ever known told me - lower is better always, always), log some baseline data, check the car, read the tires, and get some fuel consumption data. Robbie Groff used to tell me he needed the car to “talk to him” before he could tell me what we needed. Don’t screw up a good setup in the first session. Think where our driver could have qualified if he had kept the setup he ended up with and progressed forward in the sessions instead of going in a circle.
The spec car
If you have a restricted car or spec car, you have less things to try on the weekend. You should know the car well, if you have some experience with it. Otherwise, you can get a good starting set up from someone in the series. These cars are really relatively simple and require a methodical approach, rather than the shotgun approach of multiple wild guesses in search of the magic set up that gives you the 1 second you need. Now, there are some spec cars that are so bad that you do need the tricks that only the veterans know. My advice is to be prepared for a frustrating time, buy or steal the tricks, or run a real race car series.
Most series in North America have good cars that behave as expected. Try to stay within your setup window. You must define that window and keep refining it as you get to know the car better. But, resist the urge to go way out of what you know on a race weekend. Save that for testing. Keep a list of things you wanted to try at a race weekend, but did not because you did not know what it would do. Answer those questions at the next test.
On race weekends, it is always best to make changes that produce known results. If you don’t know what a change will do, go testing. If things are going well and you can afford to test for a session, then give some of the unknowns a poke. You can always go back to your baseline. Just remember, the other drivers will be moving forward in their setup when you are testing. You may find yourself behind by losing the session.
The track will tip your base setup some, but not much in a spec car. Try to come up with a base setup which will be refined each weekend. Run it at each track for the first session or two. You know how the car performs and feels with this setup, you know you liked it at the last race and there are no surprises to it. If the car feels different at this new track, you have just quantified the track. Using your base setup for the car, you can see what the track did to it. Make adjustments in the window of what you know works. Be sure the car is talking to you before you start. My driver/engineer friend likes to say “the laws of physics don’t change when you cross state lines.”
One last thing on this subject. Don’t fall into what I call the “Runoffs mistake”. A driver does a great job all year and qualifies for the prestigious SCCA Runoffs by hard work, good understanding of the car, and good procedures to get the set up right. He makes the trip to Road America and knows he has a shot to win this thing. But he knows there are some very good drivers from all over the U.S., and he thinks he needs something special to win. He finds a trick tire that he has never run but it is “worth 0.3 seconds”. The expert shock guy gave him the best Road America set up. The engine guy has the new development exhaust system. The result – the poor guy gets clobbered, not only by the out of division drivers, but also by the guys he beat all year, who now run away from him. Run what you know and tune it better than the next guy. Save the tricks for winter testing.
Changes – The secondary effects
In talking to engineers and drivers, I hear that they made a change and it did not help or did something completely different than they expected. Most of the time, the reason is what I call the secondary effect of a change.
Most racers have a good idea of what a change will do to the car, or at least they know what they want it to do. The problem is that seldom does a change only do one thing to the performance of the car. Each change has a primary effect and a secondary effect. There are third and fourth effects I am sure, but I am just barely smart enough to figure out the second effect.
If you are trying to decide between a few changes to improve something in the balance of the car, make a list of the three or four possible changes and what you expect each to do. For example, assume we have an understeer from the apex to the exit. We could change:
1 – More front wing
2 – More rake
3 – Stiffer rear springs
4 – More front rebound
There may be fifteen other things you could do, but list the top contenders. Now, list what you think the secondary effect of each might be:
1 – More front wing – oversteer in high speed turns
2 – More rake – nervous rear in high speed turns
3 – Stiffer rear springs – worse power down traction
4 – More front rebound – harsher in the bumps
Look at the list and try to find a change that has a primary effect and secondary effect that are in the same direction. Also, consider what other problems the driver may be having, which we’ll call the secondary complaint. In our example, if the high speed turns were good or bordering on oversteer, then we can eliminate the wing and rake. The stiffer rear springs will keep the dynamic rake in the car (primary effect) and free the car up on exit, while with less power down traction (secondary effect). Everything works in the direction we want.
What we want to avoid is a change with the primary effect opposite from the secondary effect. Often, this results in the driver comment of “can’t really tell much difference.” When a change has an unexpected result, you should look at the secondary effect. Sometimes, what you thought was the secondary effect was really the primary effect, and it was in the opposite direction.
Keeping track of all these effects and changes can get very confusing. The problem is that the effect of a change on a FF-1600 is very likely to be different from the same change on a Formula Atlantic car.
The change data base
There is a way to help sort the changes and what they did to your car. It helps you learn the car and can be a great tool to suggest changes that you know the result of like we talked about earlier.
One year at the test days for the Daytona 24 Hour, I was done with a session and walked past the factory Nissan NISMO team from Japan. In their pit were four racks of computers and more electronics than a modern day F1 team has. I watched for a while, as the Group C Nissan went around and around. There were only two guys manning the computer banks, so I walked up and asked what they were logging. The answer was that they were logging over 200 channels of data. I tried to think of 200 channels I would want to have logged. I got to about 30 and had to ask “what are you guys logging?” The Japanese engineer said “mostly engine parameters”. He said the engine block had twenty strain gauges cast into the block to measure stress in various sections of the block.
I thought that was very cool, but wanted to know what they were going to do with the data. The engineer said that, sometime in the future, a Nissan engineer was going to want to know what the stress was in an engine block. When that happened, the data would be there. He said that the cost of running a race car was so high, that collecting data while it was running reduced the cost of gaining that information later, when someone needed it. That impressed me with the long term thinking to collect data. Collect the data when you can, sort it out when you have time.
Any race team can do the same thing, on a smaller scale. Using a spread sheet, make a matrix with each column being a parameter in your setup. Include columns for driver comment, change, and result of the change. Each row will be a track outing. Start to log the result of each change you make to your car. In short order, you will have a history of each change made to your car.
Using the data sort function of the spread sheet, you can sort the data. For example, you can show every time you had exit understeer. Then, look at what you changed when you had that problem and what the result was. This will prevent you from making the same set up mistake twice. And, it will tell you what things have worked to correct an exit understeer in the past. It will keep you in the window of your knowledge. When testing, look at the data base and try some things that you have not tried before. This expands your understanding of the car and makes your data base more helpful at the track.
Using a data base program, like Access, takes it to the next level with tables, forms, and special queries to make the search results more meaningful and detailed. If you spend some time (it took me about 30 hours and I am NOT an Access expert), you can answer more questions. You can ask the database to show what we changed to reduce a mid corner oversteer in a third gear turn when we had tire pressures above 15 psi and a rear wing setting below 10 degrees.
Remember, the sooner you start collecting the data, the cheaper every mile you do becomes, because you are getting more value for your dollar. I can say that this has helped me a bunch over the years. My Daytona Prototype data base has over 900 changes logged in it. It just makes me a better guesser.
So, to recap…
1 – The driver is in charge of his setup. The engineer just makes the change he thinks will help him the most.
2 – Resist making changes until the driver really has a good feel for the car. It has to “talk to him” first.
3 – Physics does not change when you cross state lines. Go with what you know.
4 – The secondary effect of a change can be in the opposite of the primary effect. Never make a change without considering the secondary effect.
5 – Use a data base to increase your understanding of your car quicker and with more accuracy.
6 – If a change does not have the effect you thought it would, than you are missing some effect that you did not consider. There is not some weird phenomenon going on, you just don’t understand the circumstances of the particular situation.
7 – When in doubt, go back to your base setup and start over from there.
8 – Never copy another faster team’s setup. You need to know why yours does not work, so you can be better next time.
9 - If a change works the way you thought it would, you did not learn anything. You did become faster, which is always a good thing. But, when the change does not work as planned, you have a great chance to become smarter. Grab on to that and figure it out.
10 – When recording changes in your notes, write down why you made that change, your thinking on what you expect it to do, and why. Then, you can go back later and see what your thinking was for making that change and decide where your thinking was wrong. This may happen months later, as you get to know the car better, but it allows you to see where your mistake was, not just that it was a mistake.
OK, one more thing.
My friend, the driver/engineer mentor of mine, wrote these points down once about problem solving. Think about them. It may change your approach to finding the perfect set up.
1 – What’s right is right and everything else is wrong to some degree.
2 – What is REALLY happening here?
3 – Nothing happens for no reason.
4 – Everything is attributable.
5 – If X is true then Y must also be true. If I can’t prove that Y actually does as I predict, then I don’t know anything at all about X.
6 – What I am certain is correct can change instantly in the light of what is REALLY correct, whether I like it or not.
7 – Just because I don’t want to believe it, doesn’t make it wrong.
7a – Just because I want to believe it doesn’t make it right, either.
8 – Knowing what is wrong is every bit as important as knowing what is right.
9 – If it isn’t all the things you think it is, then it is something else. (Sherlock Holmes)
10 – You only know something if you can prove it. Everything else is “I suspect” or “I guess” or “I wonder if” or “it is my theory that...”
11 – The right answer is still the right answer even if you didn’t think of it.
12 – The right answer is still the right answer even if you don’t have any idea of why it works... but find out later for sure, because the underlying principles will always apply.
13 – Asking other people for answers is perfectly acceptable, as long as you never believe them.
He also has the dubious distinction of being the only race engineer who actually drove against me. It was a while ago... If I recall, I beat him then, but he's paid it back as an engineer, more than once.
Since we're friends, I'll indulge him for scooping me on material that was to have been included in the "Philosophy" series. But, there's much more than that in his post. I'm sure you'll find it thought-provoking.
The Setup – How to get it right
Apart from money, a good setup may be the most sought after thing in racing.
One thing before we talk about how to get the setup right. Who is ultimately responsible for the setup on the car? The driver! Not the engineers, not the team manager, not the chief mechanic, or anyone else except the driver. I hate it when people say “the engineer really has that car set up well.” It has little to do with the engineer. I have yet to see an engineer put a setup on a car, install a new driver, never change the setup, and win everything in sight. It never happens. The driver guides the setup process, he directs the engineers in the areas that need improvement, he is in charge of the car, and he has to get it to his liking to be fast. The engineer only interprets what the driver tells him and comes up with suggestions on what changes could help the problems the driver has identified as the main thing preventing him from going quicker. The engineer has the technical resources to come up with the best change to get the desired results, but he can’t identify and prioritize the areas that need improving without a technically good driver to point him in the right direction.
The magic setup – No numbers
Getting the setup right is not about cambers, toe, springs, and all the technical numbers. It is about the approach you take and the procedures you use to get there. So, I am not going to tell you the perfect springs to run at Laguna, or what wing setting works best at Montreal. Why? Because, it all depends on way too many things. I just plain don’t know the answer. What I am sure of is that, if you follow the things below, you will be ahead of the game in finding the springs or wing settings for your driver, your car, and the track on the weekend you are racing.
Best way to a great setup – Don’t change anything!
So, you spend hours with your driver and the data in the shop designing the starting setup for the weekend. You have experience with the car and kind of know the type of track you are going to, but have never been there before. You have it nailed, you think. You unload and head out for the first session. Four laps later, the driver is in the pits looking for a change. You jump in and start changing things; you want it to be better for him.
After the session you make more changes, maybe three or four, because he was 1 second off the pace. Next session the car is doing different things than before. Oh no, the changes were in the wrong direction. You remove the three changes and go the other way with four more. Now it’s better, but now a there is a different problem.
The data looks confusing, the driver is confused, but time is running out now, and you are still 0.8 seconds off. Something must be way different about this track than you thought. You decide you may have to rethink the entire setup, or that you may not really understand the car like you thought.
The next session you are better. The times are closer to fast guys and the driver just needs a few small changes. The changes help and the panic subsides some. But, you still need three tenths.
Now, it’s qualifying. The changes helped, and you’re now two tenths off the pole and on the second row. So, let’s look at the qualifying setup. It is exactly how we unloaded! We went in a big circle.
I see this all the time, at all levels of motorsport. I don’t know of any race engineers who get paid by the change. Slow down. Let the driver learn the track, and then figure out what he needs. The track will clean up and get some rubber down. Have confidence in your starting setup. Don’t be in a hurry to change it all around right away. Talk with your driver and write out a testing plan listing each session and what you hope to get done. This will only be a guide for the weekend, but it allows you to plan the sessions as you wish they would go.
A driver’s feed back is junk for the first session, anyway. He is getting a feel for the track, the grip level, and the car. Use that session to set the ride height (as the best engineer/driver I have ever known told me - lower is better always, always), log some baseline data, check the car, read the tires, and get some fuel consumption data. Robbie Groff used to tell me he needed the car to “talk to him” before he could tell me what we needed. Don’t screw up a good setup in the first session. Think where our driver could have qualified if he had kept the setup he ended up with and progressed forward in the sessions instead of going in a circle.
The spec car
If you have a restricted car or spec car, you have less things to try on the weekend. You should know the car well, if you have some experience with it. Otherwise, you can get a good starting set up from someone in the series. These cars are really relatively simple and require a methodical approach, rather than the shotgun approach of multiple wild guesses in search of the magic set up that gives you the 1 second you need. Now, there are some spec cars that are so bad that you do need the tricks that only the veterans know. My advice is to be prepared for a frustrating time, buy or steal the tricks, or run a real race car series.
Most series in North America have good cars that behave as expected. Try to stay within your setup window. You must define that window and keep refining it as you get to know the car better. But, resist the urge to go way out of what you know on a race weekend. Save that for testing. Keep a list of things you wanted to try at a race weekend, but did not because you did not know what it would do. Answer those questions at the next test.
On race weekends, it is always best to make changes that produce known results. If you don’t know what a change will do, go testing. If things are going well and you can afford to test for a session, then give some of the unknowns a poke. You can always go back to your baseline. Just remember, the other drivers will be moving forward in their setup when you are testing. You may find yourself behind by losing the session.
The track will tip your base setup some, but not much in a spec car. Try to come up with a base setup which will be refined each weekend. Run it at each track for the first session or two. You know how the car performs and feels with this setup, you know you liked it at the last race and there are no surprises to it. If the car feels different at this new track, you have just quantified the track. Using your base setup for the car, you can see what the track did to it. Make adjustments in the window of what you know works. Be sure the car is talking to you before you start. My driver/engineer friend likes to say “the laws of physics don’t change when you cross state lines.”
One last thing on this subject. Don’t fall into what I call the “Runoffs mistake”. A driver does a great job all year and qualifies for the prestigious SCCA Runoffs by hard work, good understanding of the car, and good procedures to get the set up right. He makes the trip to Road America and knows he has a shot to win this thing. But he knows there are some very good drivers from all over the U.S., and he thinks he needs something special to win. He finds a trick tire that he has never run but it is “worth 0.3 seconds”. The expert shock guy gave him the best Road America set up. The engine guy has the new development exhaust system. The result – the poor guy gets clobbered, not only by the out of division drivers, but also by the guys he beat all year, who now run away from him. Run what you know and tune it better than the next guy. Save the tricks for winter testing.
Changes – The secondary effects
In talking to engineers and drivers, I hear that they made a change and it did not help or did something completely different than they expected. Most of the time, the reason is what I call the secondary effect of a change.
Most racers have a good idea of what a change will do to the car, or at least they know what they want it to do. The problem is that seldom does a change only do one thing to the performance of the car. Each change has a primary effect and a secondary effect. There are third and fourth effects I am sure, but I am just barely smart enough to figure out the second effect.
If you are trying to decide between a few changes to improve something in the balance of the car, make a list of the three or four possible changes and what you expect each to do. For example, assume we have an understeer from the apex to the exit. We could change:
1 – More front wing
2 – More rake
3 – Stiffer rear springs
4 – More front rebound
There may be fifteen other things you could do, but list the top contenders. Now, list what you think the secondary effect of each might be:
1 – More front wing – oversteer in high speed turns
2 – More rake – nervous rear in high speed turns
3 – Stiffer rear springs – worse power down traction
4 – More front rebound – harsher in the bumps
Look at the list and try to find a change that has a primary effect and secondary effect that are in the same direction. Also, consider what other problems the driver may be having, which we’ll call the secondary complaint. In our example, if the high speed turns were good or bordering on oversteer, then we can eliminate the wing and rake. The stiffer rear springs will keep the dynamic rake in the car (primary effect) and free the car up on exit, while with less power down traction (secondary effect). Everything works in the direction we want.
What we want to avoid is a change with the primary effect opposite from the secondary effect. Often, this results in the driver comment of “can’t really tell much difference.” When a change has an unexpected result, you should look at the secondary effect. Sometimes, what you thought was the secondary effect was really the primary effect, and it was in the opposite direction.
Keeping track of all these effects and changes can get very confusing. The problem is that the effect of a change on a FF-1600 is very likely to be different from the same change on a Formula Atlantic car.
The change data base
There is a way to help sort the changes and what they did to your car. It helps you learn the car and can be a great tool to suggest changes that you know the result of like we talked about earlier.
One year at the test days for the Daytona 24 Hour, I was done with a session and walked past the factory Nissan NISMO team from Japan. In their pit were four racks of computers and more electronics than a modern day F1 team has. I watched for a while, as the Group C Nissan went around and around. There were only two guys manning the computer banks, so I walked up and asked what they were logging. The answer was that they were logging over 200 channels of data. I tried to think of 200 channels I would want to have logged. I got to about 30 and had to ask “what are you guys logging?” The Japanese engineer said “mostly engine parameters”. He said the engine block had twenty strain gauges cast into the block to measure stress in various sections of the block.
I thought that was very cool, but wanted to know what they were going to do with the data. The engineer said that, sometime in the future, a Nissan engineer was going to want to know what the stress was in an engine block. When that happened, the data would be there. He said that the cost of running a race car was so high, that collecting data while it was running reduced the cost of gaining that information later, when someone needed it. That impressed me with the long term thinking to collect data. Collect the data when you can, sort it out when you have time.
Any race team can do the same thing, on a smaller scale. Using a spread sheet, make a matrix with each column being a parameter in your setup. Include columns for driver comment, change, and result of the change. Each row will be a track outing. Start to log the result of each change you make to your car. In short order, you will have a history of each change made to your car.
Using the data sort function of the spread sheet, you can sort the data. For example, you can show every time you had exit understeer. Then, look at what you changed when you had that problem and what the result was. This will prevent you from making the same set up mistake twice. And, it will tell you what things have worked to correct an exit understeer in the past. It will keep you in the window of your knowledge. When testing, look at the data base and try some things that you have not tried before. This expands your understanding of the car and makes your data base more helpful at the track.
Using a data base program, like Access, takes it to the next level with tables, forms, and special queries to make the search results more meaningful and detailed. If you spend some time (it took me about 30 hours and I am NOT an Access expert), you can answer more questions. You can ask the database to show what we changed to reduce a mid corner oversteer in a third gear turn when we had tire pressures above 15 psi and a rear wing setting below 10 degrees.
Remember, the sooner you start collecting the data, the cheaper every mile you do becomes, because you are getting more value for your dollar. I can say that this has helped me a bunch over the years. My Daytona Prototype data base has over 900 changes logged in it. It just makes me a better guesser.
So, to recap…
1 – The driver is in charge of his setup. The engineer just makes the change he thinks will help him the most.
2 – Resist making changes until the driver really has a good feel for the car. It has to “talk to him” first.
3 – Physics does not change when you cross state lines. Go with what you know.
4 – The secondary effect of a change can be in the opposite of the primary effect. Never make a change without considering the secondary effect.
5 – Use a data base to increase your understanding of your car quicker and with more accuracy.
6 – If a change does not have the effect you thought it would, than you are missing some effect that you did not consider. There is not some weird phenomenon going on, you just don’t understand the circumstances of the particular situation.
7 – When in doubt, go back to your base setup and start over from there.
8 – Never copy another faster team’s setup. You need to know why yours does not work, so you can be better next time.
9 - If a change works the way you thought it would, you did not learn anything. You did become faster, which is always a good thing. But, when the change does not work as planned, you have a great chance to become smarter. Grab on to that and figure it out.
10 – When recording changes in your notes, write down why you made that change, your thinking on what you expect it to do, and why. Then, you can go back later and see what your thinking was for making that change and decide where your thinking was wrong. This may happen months later, as you get to know the car better, but it allows you to see where your mistake was, not just that it was a mistake.
OK, one more thing.
My friend, the driver/engineer mentor of mine, wrote these points down once about problem solving. Think about them. It may change your approach to finding the perfect set up.
1 – What’s right is right and everything else is wrong to some degree.
2 – What is REALLY happening here?
3 – Nothing happens for no reason.
4 – Everything is attributable.
5 – If X is true then Y must also be true. If I can’t prove that Y actually does as I predict, then I don’t know anything at all about X.
6 – What I am certain is correct can change instantly in the light of what is REALLY correct, whether I like it or not.
7 – Just because I don’t want to believe it, doesn’t make it wrong.
7a – Just because I want to believe it doesn’t make it right, either.
8 – Knowing what is wrong is every bit as important as knowing what is right.
9 – If it isn’t all the things you think it is, then it is something else. (Sherlock Holmes)
10 – You only know something if you can prove it. Everything else is “I suspect” or “I guess” or “I wonder if” or “it is my theory that...”
11 – The right answer is still the right answer even if you didn’t think of it.
12 – The right answer is still the right answer even if you don’t have any idea of why it works... but find out later for sure, because the underlying principles will always apply.
13 – Asking other people for answers is perfectly acceptable, as long as you never believe them.
Friday, February 5, 2010
Setup Sheets, Part 4
We'll wrap up the series on setup sheets with some specific thoughts about parts of the sheet's content. For the most part, you can refer to the basic sports prototype sheet from Part 1, reproduced below.
Sports Car Prototype Setup PDF
Tolerances
You and the crew need a mutual understanding of the tolerances for any given adjustment. There are two pieces to this. The first is your knowledge, as engineer, of what constitutes a significant change in any adjustment. The tolerance, of course, should be tight enough to avoid changing the car by missing the target. The second is the crew's ability to hit your target and your tolerances, either because of finite steps for some adjustments, or because of inability to either measure or adjust tighter than some tolerance. For example, if you call out a toe-out setting to a tolerance of .002", you are way tighter than adjustment repeatability, measurement accuracy, and large enough difference to effect the car.
Specific hardware
When you know it, call out the specific part number, hole number, shim thickness, or other part or adjustment specification that should lead to a specific setup target. The setup sheet above, for instance, is for a car with front camber slugs, rear camber shims, caster shims, and specific holes for wing adjustment. In each case, both the setup target and the hardware spec are called out on the sheet. In the event that the crew can't hit the setup target by following the hardware spec, something is either wrong or misunderstood, and discussion will be required.
Standard setup conditions
For the sake of repeatability and comparison, it helps to always set up with the certain setup conditions always the same. Tire pressures, driver weight, and fuel load are chief among these. If you're not using "setup wheels", the devoted metal fixtures that replace wheels and tires, then you should always use the same set of actual tires and wheels. Actual running conditions for the start of the session will vary. For instance, we'll set up at typical hot tire pressure, but start the session lower than that. Starting fuel load may be more or less than setup. You get the idea.
Actual vs. target
Some fields on the sheet may have spaces for actual vs. target. This is helpful if you want to record what you intended vs. how the car actually ran. The difference could be from tolerances, measurement precision, or simply error.
Corner weights
If you have a good grasp of the total weight and the percentages for front and left side, you should be able to predict the actual corner weights for any given cross weight within a couple of pounds. I tell my crew that, if they miss the target corner weights by more than a certain margin, they should contact me so we can figure out what's up.
Wings
Lots of folks call out wing angle as relative to the reference plane of the car, which is usually defined as some part of the underfloor. This seems simple enough. Time and again, though, it seems that zeroing the Smart Level against the floor isn't a totally repeatable process. I've come to call out wing angles as absolute, versus the ground. The results, for me, are more repeatable.
I learned this the hard way, in my early days in IRL. We had a flawed zero against the top of the tub floor inside the car. For part of the weekend, we struggled with lack of grip as we ran less wing angle than the series actually would have permitted us to use.
That about does it for setup sheets. Hope you've enjoyed it.
Sports Car Prototype Setup PDF
Tolerances
You and the crew need a mutual understanding of the tolerances for any given adjustment. There are two pieces to this. The first is your knowledge, as engineer, of what constitutes a significant change in any adjustment. The tolerance, of course, should be tight enough to avoid changing the car by missing the target. The second is the crew's ability to hit your target and your tolerances, either because of finite steps for some adjustments, or because of inability to either measure or adjust tighter than some tolerance. For example, if you call out a toe-out setting to a tolerance of .002", you are way tighter than adjustment repeatability, measurement accuracy, and large enough difference to effect the car.
Specific hardware
When you know it, call out the specific part number, hole number, shim thickness, or other part or adjustment specification that should lead to a specific setup target. The setup sheet above, for instance, is for a car with front camber slugs, rear camber shims, caster shims, and specific holes for wing adjustment. In each case, both the setup target and the hardware spec are called out on the sheet. In the event that the crew can't hit the setup target by following the hardware spec, something is either wrong or misunderstood, and discussion will be required.
Standard setup conditions
For the sake of repeatability and comparison, it helps to always set up with the certain setup conditions always the same. Tire pressures, driver weight, and fuel load are chief among these. If you're not using "setup wheels", the devoted metal fixtures that replace wheels and tires, then you should always use the same set of actual tires and wheels. Actual running conditions for the start of the session will vary. For instance, we'll set up at typical hot tire pressure, but start the session lower than that. Starting fuel load may be more or less than setup. You get the idea.
Actual vs. target
Some fields on the sheet may have spaces for actual vs. target. This is helpful if you want to record what you intended vs. how the car actually ran. The difference could be from tolerances, measurement precision, or simply error.
Corner weights
If you have a good grasp of the total weight and the percentages for front and left side, you should be able to predict the actual corner weights for any given cross weight within a couple of pounds. I tell my crew that, if they miss the target corner weights by more than a certain margin, they should contact me so we can figure out what's up.
Wings
Lots of folks call out wing angle as relative to the reference plane of the car, which is usually defined as some part of the underfloor. This seems simple enough. Time and again, though, it seems that zeroing the Smart Level against the floor isn't a totally repeatable process. I've come to call out wing angles as absolute, versus the ground. The results, for me, are more repeatable.
I learned this the hard way, in my early days in IRL. We had a flawed zero against the top of the tub floor inside the car. For part of the weekend, we struggled with lack of grip as we ran less wing angle than the series actually would have permitted us to use.
That about does it for setup sheets. Hope you've enjoyed it.
Monday, January 4, 2010
Setup sheets, Part 3
We now veer from the content of setup sheets to focus instead on using them. Since the setup sheet is primarily a communication tool, that will be the theme of this post. The final post will cover specific content items on the sheet.
What happens on the first usage of a new setup sheet?
Some teams want you, as a newly-arrived engineer, to use their existing setup sheet. OK, then get on with it. If you need to make changes to the sheet, phase them in as needed, with agreement of all concerned. No surprises allowed.
Other teams will allow you to use your own format. Or, maybe, you've decided to rework the existing format. In either case, it's absolutely essential to sit down with the crew and review the format and content of the setup sheet. The compressed layout needed to convey so much information will almost certainly lead to misunderstandings if you bypass this step. Remember, communicate!
When does the setup sheet need to be done?
Let's talk about the pre-event sheet first. You could wait until a day or two before the car goes on the setup pad. You'll probably only get one or two opportunities to do that, though, before someone gives strong verbal feedback, or worse.
On the engineering side, we often want to review notes and data from the previous event before deciding how to set up for the next event. Maybe we've got wind tunnel or 7-post testing coming soon, too. Maybe some significant analysis or simulation work will reach conclusions soon. All this work could have a significant effect on the setup, and not just on adjustments. We may need to make (and test-fit) aero or chassis parts, revalve shocks, buy parts, and more.
Meanwhile, the team typically has a limited amount of time to turn the car around. There will be a finite amount of manpower available to deal with changes. And, all this will usually happen on a schedule without much wiggle room.
What happens on the first usage of a new setup sheet?
Some teams want you, as a newly-arrived engineer, to use their existing setup sheet. OK, then get on with it. If you need to make changes to the sheet, phase them in as needed, with agreement of all concerned. No surprises allowed.
Other teams will allow you to use your own format. Or, maybe, you've decided to rework the existing format. In either case, it's absolutely essential to sit down with the crew and review the format and content of the setup sheet. The compressed layout needed to convey so much information will almost certainly lead to misunderstandings if you bypass this step. Remember, communicate!
When does the setup sheet need to be done?
Let's talk about the pre-event sheet first. You could wait until a day or two before the car goes on the setup pad. You'll probably only get one or two opportunities to do that, though, before someone gives strong verbal feedback, or worse.
On the engineering side, we often want to review notes and data from the previous event before deciding how to set up for the next event. Maybe we've got wind tunnel or 7-post testing coming soon, too. Maybe some significant analysis or simulation work will reach conclusions soon. All this work could have a significant effect on the setup, and not just on adjustments. We may need to make (and test-fit) aero or chassis parts, revalve shocks, buy parts, and more.
Meanwhile, the team typically has a limited amount of time to turn the car around. There will be a finite amount of manpower available to deal with changes. And, all this will usually happen on a schedule without much wiggle room.
It isn't really possible to say exactly how long ahead of the next event you need to be done. The correct answer is "it depends".
- Are you taking the same car to the next race as the previous one?
- How time-consuming are the changes envisioned, beyond simple parts swapping and adjustments?
- When does the car need to go in the trailer? How far ahead of that must the car be set up?
- How important are the non-adjustment changes, in terms of performance potential? How sure are you of their value, and how sure is the crew of their ability to complete them?
- How "non-routine" will the setup pad work be?
I can't, repeat cannot, overemphasize the importance of communication with the crew. If you envision changes, then you absolutely must discuss them well in advance of actually asking for them. Jointly review their probability of actually happening, the work required to accomplish them, when you can realistically have them defined, and what the possible pitfalls might be. Then, jointly decide on a plan.
A few thoughts:
- The optimal time for the setup sheet to arrive is just before reassembly of the car begins, and with enough lead time for all the changes.
- It may help to produce a preliminary setup, to be revised as engineering work finishes. Be advised, this approach is full of pitfalls and requires a clear understanding from everyone involved.
- When the races are coming hot and heavy, maybe on back-to-back weekends, you're likely to have to prepare setups for several races ahead of yourself.
Here's a clue - when the crew is consistently asking you for a setup, then either you are too late producing them, or they want them too far in advance. Talk with each other, figure out the situation, and fix it.
How to deliver the setup sheet?
I prefer to add a "cover memo" to draw attention to anything important. Maybe you're changing something that has remained constant for a long time. Maybe there are exercises to be done on the setup pad, or some specific instructions on how to do part of the setup. It's easy to have this discussion verbally, but there's always some risk of misunderstanding.
Now, what about between sessions at the track?
The basic situation between sessions is much like the pre-event setup, only compressed in time. As an engineer, you want to debrief the driver, look at some data from the car, punch some numbers into the calculator or software, and maybe crank out a sim run or two. The crew wants to get the car ready for the next session. Here's how you do it:
On the way back to the paddock or the garage, tell the crew chief whether you need a setdown. If not, then he can start on the maintenance issues while you work on the setup. Tell him what changes you're considering, if it entails a significant job (for instance, changing brake master cylinders can be a challenge on some cars), and agree on whether the change needs to happen now or can wait until the end of the day. Changing ratios in the gearbox, for instance, typically needs some lead time - you know you're going to do it, even if you don't know what ratios to install yet. Finally, agree on when he needs your final answer on the changes you just discussed.
Spend the rest of the walk back deciding if you can call out the setup changes NOW. If you can, you are now officially a hero.
Put out a job list for the crew, DAG, shock guy, etc. immediately after arriving at the paddock or garage. No ifs, ands, or buts.
Get into your job deciding on the setup changes with energy and focus. Debrief, analyze, and decide. Now. Take it as a personal challenge to avoid agonizing over decisions. This is going to sound brutal, but if you repeatly have to agonize over the setup, then you either aren't ready for the job or you aren't decisive. Either that, or there's something you haven't learned about the car and desperately need to figure out.
If you spend two hours fussing over the setup, with the crew waiting on you and the next session looming, only to decide on a big change like tearing into the gearbox (stressing the crew) or a trivial one like a minor spring change (insulting the crew), you are not a hero, and will not be able to repeat this behavior forever - unless you and the driver win a lot of races!
Once you've decided, communicate your setup changes clearly and concisely. I found out, the hard way, that a new full setup sheet IS NOT the way to do this between sessions. There is too much information on it for the crew to pick through, while searching for the changes. I simply provide a list of the changes. Sometimes the setup worksheet from the previous post in this series is a good way to do this, sometimes it goes on the job list. It's best to discuss it with the crew chief, no matter what format you use. Avoiding misunderstandings is the goal.
That's about it for today.
Wednesday, December 30, 2009
DOE in NASCAR Sprint Cup
Brandon Thomas is Chief Design and Development Engineer for Red Bull Racing in NASCAR. He has the dubious distinction of being the first victim to be drafted for a guest blog on The Race Engineer. Thanks a bunch, Brandon. Without further ado...
I feel honored to be invited to guest blog on The Race Engineer blog. I made the mistake of updating my LinkedIn profile with some obscure details of my work history and Buddy came calling. He and I have traded EMails over the last few weeks, and some of that content he felt was worthy of the blog. So, here goes.
DOE, design of experiment, was a topic briefly glossed over in my required statistics and probability class during engineering school. Had it been more of a focal point in the class, I probably would have paid much more attention. Seems the biggest problem educators have is making the course content relevant to the audience. I cannot explain the intricacies, or even the theory, behind the method in a simplified discussion. The point of DOE is to build a response model based on several user-decided factors. Like all models, it requires the user to be pretty informed ahead of time of what is expected in the results, but also to be somewhat open-minded when the results diverge from the expected. I’ll leave it up to you readers to do more research on the www on the method and its origins.
DOE was certainly revered in the pharmaceutical industry – probably still is. Types of experiments, the number of factors involved, and the complexity of the experiment are all parts of drug trials in this era. What does that have to do with making your racecar go faster around a given lap than the competition? Working smarter, not harder, eliminating the surrounding static, and concentrating on the most important setup parameters to achieve a result.
In this realm, I am alluding to a method of DOE involving simulation code. There are many basic advantages to DOE in the virtual world. The repeats can all be skipped, the number of factors can be rather large, and you can accomplish a full factorial design with today’s larger multi-core machines. There are other methods of DOE outside the virtual world, but I’ll take the academic copout that those are beyond the scope of this blog, and are sensitive information in a competitive environment.
Now let’s get to the good stuff. What does DOE methodology do for the race engineer?
One of the most useful tools to a race engineer when away from the computer is a Pareto chart based on the results of the DOE. Here’s an entirely fake example of one.
I feel honored to be invited to guest blog on The Race Engineer blog. I made the mistake of updating my LinkedIn profile with some obscure details of my work history and Buddy came calling. He and I have traded EMails over the last few weeks, and some of that content he felt was worthy of the blog. So, here goes.
DOE, design of experiment, was a topic briefly glossed over in my required statistics and probability class during engineering school. Had it been more of a focal point in the class, I probably would have paid much more attention. Seems the biggest problem educators have is making the course content relevant to the audience. I cannot explain the intricacies, or even the theory, behind the method in a simplified discussion. The point of DOE is to build a response model based on several user-decided factors. Like all models, it requires the user to be pretty informed ahead of time of what is expected in the results, but also to be somewhat open-minded when the results diverge from the expected. I’ll leave it up to you readers to do more research on the www on the method and its origins.
DOE was certainly revered in the pharmaceutical industry – probably still is. Types of experiments, the number of factors involved, and the complexity of the experiment are all parts of drug trials in this era. What does that have to do with making your racecar go faster around a given lap than the competition? Working smarter, not harder, eliminating the surrounding static, and concentrating on the most important setup parameters to achieve a result.
In this realm, I am alluding to a method of DOE involving simulation code. There are many basic advantages to DOE in the virtual world. The repeats can all be skipped, the number of factors can be rather large, and you can accomplish a full factorial design with today’s larger multi-core machines. There are other methods of DOE outside the virtual world, but I’ll take the academic copout that those are beyond the scope of this blog, and are sensitive information in a competitive environment.
Now let’s get to the good stuff. What does DOE methodology do for the race engineer?
One of the most useful tools to a race engineer when away from the computer is a Pareto chart based on the results of the DOE. Here’s an entirely fake example of one.
In this case we decided to look at roll angle and the effects each of these basic factors have on the vehicle roll angle at a given point on the racetrack that we have decided as being critical. Did you see the number of times I mentioned the end user being involved in choosing how to analyze this data? Pay attention to that sentence again. The effectiveness of a DOE approach is only as sharp as the person implementing it. There are numerous pitfalls here.
- Where do you look at the data on the track?
- What vehicle response(s) are critical to improving laptime?
- What factors were deemed critical enough to vary in the design?
- How many factors were varied?
- Was the design setup to include interaction of factors?
- In brutal honesty – how well does your simulation capture the response of your car?
- Will your setup stay close enough to the baseline that the DOE remains relevant?
You can see that, in order to effectively use this approach, you have to already have a good deal of knowledge of what you expect the outcome to be. You also have to be willing to accept when results are counterintuitive. I mentioned above about interactions, as you use higher order designs you began to capture interactions between your factors. This typically is when the human brain starts lagging in understanding – how does the engineer at the window of the car during practice comprehend how an interaction between all 7 factors listed above would affect the performance? This is when you must be back in front of the computer with the response surface calculation tool. The Pareto chart just helps you change front bar rate or the RR spring when the driver says the car rolls too much or too little – and don’t worry about the LF spring it won’t help here no matter how much you want it to. As in all real life, the previous example has a big “but” in it. What if your sim method doesn’t handle spring preload, bar preload, or jacking changes properly? Or maybe LF spring does affect roll, but you’ve just misled yourself away from that. Losing sucks, and being wrong is the geek’s version of losing.
Where do you look at the data on a given lap? Great question. This has huge implications on the quality of the fits, the impact on the setup, and the dreaded compromises that arise in any setup choice. This is trial and error, and no sane person would help a fellow competitor through this stage. Ever wonder why there are very few good SAE papers on racecar topics?
What vehicle responses are the most critical to improving lap time? When it comes to big stock cars (the vast majority of my time has been spent here), simply reducing roll angle isn’t going to make your car faster than everyone else’s, so the above example is a little off target. Simply matching dynamic crossweight to some magical number in the driver's and crew chief’s heads isn’t going to get it done either. The responses calculated are only limited by your imagination as to what defines better performance.
- What factors were deemed critical enough to vary in the design?
- How many were varied?
As the number of factors increases, so does the number of trials needed to capture the interactions of these factors. Think exponentially. This is where the multimode machines are making serious headway, no difference from CFD. What is important to your vehicle setup? What data about your model are clear enough to capture subtle changes? We all wish that tire data could be discreet to the point of being able to gnash our teeth endlessly over a very small pressure change. Vary inner and outer tire pressures (for a total of 8 factors and only 2 settings of each) in a full factorial DOE, and you’ve just signed up for 256 runs of simulation. Add only two more factors (let’s say front springs at only 2 levels) and that total is now 1024 runs. How fast is your PC? How accurate is that tire data in quantifying some change in the car? That may be better served by trying it with the driver strapped in and let the lap times make the call, except every major sanctioning body is trimming practice time as the years go by. When setting up your factors and their levels of variance, you have to allow a wide enough range to be helpful but not so wide that the response from one setting to the next is so different that the regression looks like a total mess. Maybe two levels of each factor aren’t enough, certainly when you are considering a spring change. No race team running for the big foam check at the end of the day brings only four spare springs! Now, consider that you decide you need to vary each of your 10 factors in 5 discreet values. That seems pretty reasonable. Put on your big boy pants, because you have just created a design with 9,765,625 simulation runs. Google fractional DOE design.
How well does your simulation capture the response of your car? As you can tell from the above discussion, this isn’t a topic to apply to your first runs in simulation. Get the validation work done, shoot holes in the data, and convince yourself that you are getting close. The alternative is wasting your time, which in this business tends to lead to unemployment.
You spent all week setting up the design and writing the script file to launch the sims and the array of CPUs burned through night and day without any interrupts in power or crashes in solution. Yeah, right, wait till you see some of the setups a five level full factorial design generates to run – you’ll be lucky if it can statically solve enough of them. On the final setup day, a decision is made to change the RF suspension geometry significantly. You now have a nice memorial to a lot of wasted time and effort. Once the setup winds its way outside of major parameters, the DOE becomes irrelevant. It’s a fact of life in this arena, you won’t be the first, second, or even 100th person this has happened to. The driver and team manager really aren’t going to want to hear about this. So, don’t bother. These are things that only other engineers are going to be sympathetic to, when we gather at the back of the garage to enjoy a Red Bull and complain to each other without giving away current projects.
DOE isn’t anything new. In reality, most of us were just waiting on hardware and software to catch up to concepts so it could be used. Most of my experience working on this topic happened between 1998 and 2004. The cost of such toys usually limits this approach to the big budget series. The tidbits and sarcastic remarks I have made all relate to working on this approach strictly in NASCAR Sprint Cup Racing at a couple of top level teams. I didn’t invent any of this. Like everything in racing, all of us claim to have invented it. My particular experiences happened while I was a part of a great group of engineers at previous teams. I have lived on every side of the race engineer role for the last decade, sometimes as an engineer helping support the race engineer’s job, sometimes as the race engineer, and sometimes as a crew chief using the race engineer to get the best out of the car, as quickly as possible. Luckily, my day job has nothing to do with simulation code, DOE, or race engineering these days, because this doesn’t even scratch the surface. I can guarantee you that all of the unknown faces in the Cup garage engineering these cars understand 100% of what was discussed here, and have for some time. Plenty of books have been written on the topic. I’ll leave you to go find them.
Thanks for reading,
Brandon Thomas
Red Bull Racing (USA)
Chief Design and Development Engineer
Tuesday, December 29, 2009
Setup Sheets, Part 2
Let's review the setup sheet layout. There are two fundamental layout concepts: by topic and by car location.
Sheets laid out by topic group similar items together. All the ride heights are together, all the shock info together, all the aero info together, and so on. For example, here's a prototype sports car sheet. This layout, although well done, omits some detail on brakes, tires, suspension geometry. It is used with "setup wheels", machined aluminum fixtures that replace real wheels and tires on the setup pad. Ride heights are calculated from measured drops to a point on top of the chassis, rather than actual measurements up from setup pad to the floor. Blue items are user input.
PDF - Print or Free DownloadXLS - Purchase Full Download
Sheets laid out by car location group information into a birds-eye view of the car. For each corner, you have alignment, tire data, springs, and so on. Information that doesn't fit that layout is placed on the center of the sheet or in a separate section. In a slightly different twist, the sheet that I use has chassis-mounted items and measurements like AR bars, ride heights, and packer gaps in the center, reducing the amount of info listed at the individual wheel. Here's a Swift 008a Formula Atlantic sheet. Note that this sheet includes some engineering calcs. It also has non-printing separate worksheets for vehicle dynamics and for shock build specs.
PDF - Print or Free DownloadXLS - Purchase Full Download
So, which layout to use? Both are popular, and both can be effective, if they are done well.
The main advantage of the topic layout is in grouping similar items together. For example, all the corner weights are in one spot, just like on the scale display. With so many different types of data to show, it can be a little scattered, unless it is carefully organized. The example posted here is one of the better ones.
The strength of the car location layout is in its ease of use. If you want to know something about the right front corner of the car, look at that part of the sheet. Some items, like brakes, corner weights, rake, or cooling, don't fall into the layout that well.
I use a layout that mixes some elements of both approaches. Go back and look at the sports car sample included in the Part 1 post, it's mine. Stuff mounted or measured at the wheels is out on the corners. Stuff mounted or measured on the chassis is down the middle. Front aero is at the front, rear aero at the rear. Gears, brakes, and weights are clumped together at their approximate location on the car. The next incarnation might get a new section for configuration file names for the data system, ECU, ABS, paddle shift system, etc.
Now, let's look at a layout for the worksheet that accompanies the car to the setup pad. This worksheet is a hands-on working document for use at the setup pad. Most of the teams I work with lack either the time, money, or resources for this to be used as a networked document on an smart phone or touch-screen PC. So, it's filled out by hand, and may or may not be scanned, depending on who needs copies and when. I like the cheap HP all-in-one printer/scanner/copier units for the trailer.
On the front, there are fields for Setdown, where we document how the car was found as it rolled off the track and onto the setup pad after preceding on-track session. The center column is used to enter the changes to make. The changes are then made, on or off the pad, and the car rolled on for adjustment. And then, the righthand column documents how the car rolled off the setup pad. On the back side, there is a worksheet for actually making the adjustments.
Yeah, I know, there's some redundency here, and opportunity to introduce error. We'll talk about this again in a later post, but cutting to the chase, I've found that a complete setup sheet doesn't work too well for calling out between-session changes. So, we do a setdown, fill in the changes, and finish the setup.
The example below is a scan of both the front and back pages of a setup worksheet after use. The links immediately above the form will download it, as well as blank versions of the front and back pages.
PDF - Print or Free Download Blank Form
XLS - Purchase Full Download Blank Form
PDF - Print and Free Download Completed Form
Tools and organization
OK, how about computing tools? Your choices are basically spreadsheet or data base. PDF forms with fillable fields don't have enough function. Spreadsheets offer plenty of formatting and calculating power, and are the near-universal solution. But, I've always wanted to try a database. The initial setup would be lot more work, but your setups would be available for the full power of database searching and reporting. I suspect that the ever-evolving nature of much racing might be responsible for the relative rarity of databases, since last year's setup is often no longer relevent. Series where you take the same basic car back to the same tracks, year after year, probably stand to benefit the most.
One thing is for sure. You have got to be diligent and organized in file naming and directory structure, or you will soon have an unworkable jumble of setup sheets files. Here's the file naming convention that I use:
Setup Seb090307 A04 P1 Start.xls
Sheets laid out by topic group similar items together. All the ride heights are together, all the shock info together, all the aero info together, and so on. For example, here's a prototype sports car sheet. This layout, although well done, omits some detail on brakes, tires, suspension geometry. It is used with "setup wheels", machined aluminum fixtures that replace real wheels and tires on the setup pad. Ride heights are calculated from measured drops to a point on top of the chassis, rather than actual measurements up from setup pad to the floor. Blue items are user input.
PDF - Print or Free DownloadXLS - Purchase Full Download
Sheets laid out by car location group information into a birds-eye view of the car. For each corner, you have alignment, tire data, springs, and so on. Information that doesn't fit that layout is placed on the center of the sheet or in a separate section. In a slightly different twist, the sheet that I use has chassis-mounted items and measurements like AR bars, ride heights, and packer gaps in the center, reducing the amount of info listed at the individual wheel. Here's a Swift 008a Formula Atlantic sheet. Note that this sheet includes some engineering calcs. It also has non-printing separate worksheets for vehicle dynamics and for shock build specs.
PDF - Print or Free DownloadXLS - Purchase Full Download
So, which layout to use? Both are popular, and both can be effective, if they are done well.
The main advantage of the topic layout is in grouping similar items together. For example, all the corner weights are in one spot, just like on the scale display. With so many different types of data to show, it can be a little scattered, unless it is carefully organized. The example posted here is one of the better ones.
The strength of the car location layout is in its ease of use. If you want to know something about the right front corner of the car, look at that part of the sheet. Some items, like brakes, corner weights, rake, or cooling, don't fall into the layout that well.
I use a layout that mixes some elements of both approaches. Go back and look at the sports car sample included in the Part 1 post, it's mine. Stuff mounted or measured at the wheels is out on the corners. Stuff mounted or measured on the chassis is down the middle. Front aero is at the front, rear aero at the rear. Gears, brakes, and weights are clumped together at their approximate location on the car. The next incarnation might get a new section for configuration file names for the data system, ECU, ABS, paddle shift system, etc.
Now, let's look at a layout for the worksheet that accompanies the car to the setup pad. This worksheet is a hands-on working document for use at the setup pad. Most of the teams I work with lack either the time, money, or resources for this to be used as a networked document on an smart phone or touch-screen PC. So, it's filled out by hand, and may or may not be scanned, depending on who needs copies and when. I like the cheap HP all-in-one printer/scanner/copier units for the trailer.
On the front, there are fields for Setdown, where we document how the car was found as it rolled off the track and onto the setup pad after preceding on-track session. The center column is used to enter the changes to make. The changes are then made, on or off the pad, and the car rolled on for adjustment. And then, the righthand column documents how the car rolled off the setup pad. On the back side, there is a worksheet for actually making the adjustments.
Yeah, I know, there's some redundency here, and opportunity to introduce error. We'll talk about this again in a later post, but cutting to the chase, I've found that a complete setup sheet doesn't work too well for calling out between-session changes. So, we do a setdown, fill in the changes, and finish the setup.
The example below is a scan of both the front and back pages of a setup worksheet after use. The links immediately above the form will download it, as well as blank versions of the front and back pages.
PDF - Print or Free Download Blank Form
XLS - Purchase Full Download Blank Form
PDF - Print and Free Download Completed Form
Tools and organization
OK, how about computing tools? Your choices are basically spreadsheet or data base. PDF forms with fillable fields don't have enough function. Spreadsheets offer plenty of formatting and calculating power, and are the near-universal solution. But, I've always wanted to try a database. The initial setup would be lot more work, but your setups would be available for the full power of database searching and reporting. I suspect that the ever-evolving nature of much racing might be responsible for the relative rarity of databases, since last year's setup is often no longer relevent. Series where you take the same basic car back to the same tracks, year after year, probably stand to benefit the most.
One thing is for sure. You have got to be diligent and organized in file naming and directory structure, or you will soon have an unworkable jumble of setup sheets files. Here's the file naming convention that I use:
Setup Seb090307 A04 P1 Start.xls
- Sebring is the track
- March 7, 2009 is the race date (not the creation date of the setup sheet)
- Chassis number A04
- This sheet shows how the car started the first official practice session
I place all the sheets for an event into a directory exclusive to that event. Use real-time archival software pointed at the location of all the setup sheets. You don't want to lose a year's worth of setups when the notebook hard drive crashes at the track.
Remembering that a setup sheet is a vehicle for communication, the next post will get into the process of using it. Once that's done, we'll dig deeper into content.
Monday, December 28, 2009
Setup Sheets, Part 1
I'm kinda excited about this multi-part series, since it's a bit of a departure from recent posts. We're going to review setup sheets in fairly complete detail, so this isn't your usual short-attention-span blog post. You'll be able to download PDF samples and working Excel spreadsheets from Scribd. Here we go...
What is a setup sheet, anyway?
In simple terms, it is a document that details the configuration and adjustment of a race car.
And what is it used for?
What is a setup sheet, anyway?
In simple terms, it is a document that details the configuration and adjustment of a race car.
And what is it used for?
- Define all the setup adjustments, like alignment, ride height, etc.
- Specify commonly swapped parts, like springs, gear ratios, anti-roll bars, etc.
- Document the car setup, for later reference
- Possibly, link to analysis or simulation software to provide vehicle dynamics details
The simplest setup sheets are handwritten onto a basic blank form. In this guise, it is mainly a working document for crew adjustments to the car on the setup pad. It probably has no more than the following content, and maybe less, depending on what items may be non-adjustable, non-changeable, or non-existent on a specific car:
- Ride heights
- Spring rates
- Anti-roll bar sizes and adjustments
- Shock adjustments and gas pressures
- Camber, caster, and toe settings
- Aero adjustments, such as angles and dimensions
- Corner weights and percentages
Here's the catch. If the setup sheet is to be a complete and unambiguous definition of how the car is configured, there is inevitably more information required. Sometimes, lots more. The possible list is endless, but here are some common items, in no particular order:
- Bump rubber spec and packer gaps
- Third spring and damper components and adjustments
- Optional aero components and how they are installed or adjusted
- Cooling configuration, both components and blanking
- Gear ratios and differential setup
- Optional suspension geometry and components
- Brake components, pad/rotor material, master cylinders, bias setup
- Multiple ride heights - aero components vs. structural/suspension
- Specific assembly instructions - part numbers, shims, etc.
- Tire sizes, compounds, and constructions
- Tire pressures for both the setup pad and the grid
- Driver weight and fuel load for the setup pad, starting fuel load for the track
- Shock build spec
- Part numbers or serial numbers for specific components and assemblies
- Spring and/or pushrod installed length. Rocker ratio and position.
- Ballast weight, configuration, position
This can get out of hand. Still, we absolutely have to be able to completely and unambiguously define how the car is expected to be configured when it rolls onto the track. At some time in the future, we need to be able to completely and unambiguously recall that configuration by reviewing the setup sheet.
Taking things a step further, there are two additional types of information that sometimes show up on setup sheets. They are specific component serial numbers, for use in part lifing, and vehicle dynamics calculations, such as wheel rates. I personally choose not to include these on my setup sheets. They aren't essential to defining the car configuration and clutter up its use by the crew. If needed, I think they should be on a separate document, or an "engineer's version" that can be separately printed.
We have to remember that a race car is always changing, and we race or test it as a snapshot in time. Some of these evolving changes are permanent, some not. They rarely seem to fit the existing format for the setup sheet. We have to decide whether, when, and how to indicate these changes on the setup sheet. I tend to mention permanent modifications in the comments section at the time they first appear, then delete them on future sheets - a solution I'll admit to being imperfect.
Sharp readers will have noticed no mention so far of engine configuration and tuning, nor of configuration options and file names for ECUs, data acquisition, traction control, no-lift shift, ABS, or any other electronic systems. Engines tend to be assembled, tuned, and maintained by a separate group which may or may not be part of the team. The electronics are typically maintained and tuned by one or more specialists, a process that can be a bit undisciplined, if nonetheless superbly executed. In an oddity of how things have evolved, the setup sheet is typically the configuration for the rest of the car.
One possible solution to some of these concerns is a "build sheet", produced either as a separate document or as a different print option, similar to what we've discussed for components and engineering data. It can include all sorts of information, like serial numbers, part numbers, modifications, file names, and so on.
So, here's my recommendation:
Use a comprehensive setup sheet that defines everything adjustable or changeable on the race car. Permanent modifications are either excluded or get a mention in the notes section at the time they are done. If it's appropriate for your situation, create a separate build sheet, either to define the car more fully or for part serial numbers. Keep engineering calcs off the main sheet. A worksheet accompanies the car to the setup pad for note-taking during the setup process.
To give you something to think about until the next post, here's a recent sports car racing prototype setup sheet. This sheet is fairly comprehensive, yet this car lacks certain suspension geometry and aero options that I've had on other recent setups. Numbers and other fields, of course, are changed to disguise the real setup. Fields calculated internally by the setup sheet show in blue. If you purchase the full XLS, you'll see the non-printing calcs for ride heights and gears.
Friday, December 25, 2009
Using Scribd
Hi folks.
There's a major new series coming for the Race Engineer blog. We'll be covering setup sheets in quite a bit of detail.
And, we're going to offer content for download in the Setup Sheet series, as well as in future ones. I'll be using http://www.scribd.com/. If you're not familiar with the site, it's sort of analogous to iTunes, only for documents instead of music and video.
Every document will be available free as a PDF, either to print or download. Not free beer, not free lunch, but the best I can do in a blog.
Many will also be available for purchase in the native format, which will typically be XLS. For forms with a lot of formatting and information, like setup sheets, this will save quite a bit of time compared to creating your own version from scratch. For real engineering tools, you get all the calcs behind the visible input and results.
I puzzled some over pricing. Some of this stuff is pretty simple, but some of it represents literally days, if not weeks, of work. Radiohead's pricing strategy of letting the user decide how much to pay was intriguing, but Scribd doesn't work that way. I do need to get something for my effort, but on the other hand I want to make this stuff widely available. In the end, I decided to make the forms $10 each, unless they are really simple. You're already paying that for an album download on iTunes or Amazon. And it's waaaaay cheap compared to the time you'd spend duplicating it. Real engineering tools will be priced according to their content.
The imbedded PDFs will display a frame from Scribd. Preceding each will be two links, one to the PDF, one to the native format.
Click the PDF link to print or get the free download.
Click the native format link to purchase. There will be a big yellow button "Buy Now" on the right side of the screen which takes you to the typical online purchase dialog to enter your credit card info.
The Scribd site asks you to register to get the free download or print. Wish they didn't do that, but at least it's free. Oh well...
As a sample, here's a setup sheet for an IRL car in 1998. Left or right click on the Scribd window to activate the various controls, zoom, and so on.
PDF - Print or Free Download
XLS - Purchase Download
Please drop me a comment if all this doesn't work correctly for you.
There's a major new series coming for the Race Engineer blog. We'll be covering setup sheets in quite a bit of detail.
And, we're going to offer content for download in the Setup Sheet series, as well as in future ones. I'll be using http://www.scribd.com/. If you're not familiar with the site, it's sort of analogous to iTunes, only for documents instead of music and video.
Every document will be available free as a PDF, either to print or download. Not free beer, not free lunch, but the best I can do in a blog.
Many will also be available for purchase in the native format, which will typically be XLS. For forms with a lot of formatting and information, like setup sheets, this will save quite a bit of time compared to creating your own version from scratch. For real engineering tools, you get all the calcs behind the visible input and results.
I puzzled some over pricing. Some of this stuff is pretty simple, but some of it represents literally days, if not weeks, of work. Radiohead's pricing strategy of letting the user decide how much to pay was intriguing, but Scribd doesn't work that way. I do need to get something for my effort, but on the other hand I want to make this stuff widely available. In the end, I decided to make the forms $10 each, unless they are really simple. You're already paying that for an album download on iTunes or Amazon. And it's waaaaay cheap compared to the time you'd spend duplicating it. Real engineering tools will be priced according to their content.
The imbedded PDFs will display a frame from Scribd. Preceding each will be two links, one to the PDF, one to the native format.
Click the PDF link to print or get the free download.
Click the native format link to purchase. There will be a big yellow button "Buy Now" on the right side of the screen which takes you to the typical online purchase dialog to enter your credit card info.
The Scribd site asks you to register to get the free download or print. Wish they didn't do that, but at least it's free. Oh well...
As a sample, here's a setup sheet for an IRL car in 1998. Left or right click on the Scribd window to activate the various controls, zoom, and so on.
PDF - Print or Free Download
XLS - Purchase Download
Please drop me a comment if all this doesn't work correctly for you.
Thursday, October 29, 2009
Vehicle Dynamics, Vol. 1 - Thinking in 3 Dimensions
At the outset, I promised that this blog wouldn't be a vehicle dynamics tutorial. Still true. Get out your Milliken, Gillespie, and even Carroll Smith's timeless "Tune to Win".
But, here's an observation.
When many race engineers and chassis tuners think about handling, they focus heavily on roll moment and roll stiffness. That's a vital topic, but it's only part of the total handling equation.
The car operates in 3-dimensional space, with forces and moments acting on it along the X, Y, and Z axes (longitudinal, lateral, and vertical to regular mortals). At any point in time, its handling is dependent on how it reacts to ALL SIX of those forces and moments. Limiting your thinking to roll only addresses lateral forces and longitudinal moments.
For example:
1-Savvy oval track engineers have long been focused on the vertical forces from both banking and aerodynamics.
2-When a car is cornering, it is rotating around its Z (vertical) axis. The are a number of very significant sources of moments around that axis, some of which are under the control of the engineer.
There is much to be learned from data acquisition. Install a steering travel potentiometer calibrated in spindle degrees. Install a 3-axis accelerometer and a yaw rate sensor. Just in the Z-axis, you can calculate understeer gradient (see Gillespie), yaw gain (yaw rate divided by steering), and stability index (see Danny Nowlan's excellent recent series in Race Car Engineering magazine). Use your imagination. There's more.
Apologies for the lack of illustrating diagrams. I'm still too busy with real work to explore the tools that Blogspot offers. Eventually.
The proverbial word to the proverbial wise should be sufficient. Go for it!
But, here's an observation.
When many race engineers and chassis tuners think about handling, they focus heavily on roll moment and roll stiffness. That's a vital topic, but it's only part of the total handling equation.
The car operates in 3-dimensional space, with forces and moments acting on it along the X, Y, and Z axes (longitudinal, lateral, and vertical to regular mortals). At any point in time, its handling is dependent on how it reacts to ALL SIX of those forces and moments. Limiting your thinking to roll only addresses lateral forces and longitudinal moments.
For example:
1-Savvy oval track engineers have long been focused on the vertical forces from both banking and aerodynamics.
2-When a car is cornering, it is rotating around its Z (vertical) axis. The are a number of very significant sources of moments around that axis, some of which are under the control of the engineer.
There is much to be learned from data acquisition. Install a steering travel potentiometer calibrated in spindle degrees. Install a 3-axis accelerometer and a yaw rate sensor. Just in the Z-axis, you can calculate understeer gradient (see Gillespie), yaw gain (yaw rate divided by steering), and stability index (see Danny Nowlan's excellent recent series in Race Car Engineering magazine). Use your imagination. There's more.
Apologies for the lack of illustrating diagrams. I'm still too busy with real work to explore the tools that Blogspot offers. Eventually.
The proverbial word to the proverbial wise should be sufficient. Go for it!
Thursday, October 22, 2009
Modifying Production Suspension Geometry
Well, after literally weeks of not having the time to do a new blog post, I was looking forward to a new post on testing. I'd even spent two whole airline flights outlining it.
But then, today, I had a rush job to prepare some modifications to the geometry of a production-based race car. And, surprisingly, that project generated the theme for a new blog entry. So, here we go...
We'll conveniently assume that you have already measured the car (probably a whole blog post of its own) and that you are already up and running with kinematics software. Bill Mitchell is an old friend, and I've used his programs for years.
The starting point to the whole process is learning what changes the race series rules will allow.
If the rules allow modifying or replacing the spindle/upright, you are most of the way to a from-scratch design. The steering geometry will be yours to invent, as well as most of the instant center-related items like camber gain and static roll center location. The series rules on inner pickup points will mainly handicap the ability to design the desired anti-squat or anti-dive, and will likely effect roll center migration.
If you're stuck with using the original upright geometry (with or without a usually tight spec on allowed modifications), then the freedom to improve the goemetry is much more constrained.
So, here's the basic situation:
-You will never be able to get a geometry with optimized roll center location and movement, camber gain, anti- geometry, steering geometry, and spring/shock motion ratio. Give up on that notion.
-The series rules and the car's original geometry will limit your options.
-It's pretty common that a geometry modification that helps you reach one of your targets will hurt your ability to reach another.
So, it follows that the MOST important job is NOT necessarily the design itself. It is, instead, successfully figuring out what change is most important for your car. For example, is it more important to lower the roll center, increase the anti-dive, or reduce the camber gain? Having decided what change is most important for your car, then it's time to review whether the almost-unavoidable tag-along changes will hurt the car, and understand how and how much they will hurt it. Finally, consistent with the theme of many of my posts, you will now hear me say that experience and education will only improve your chances of identifying what the car needs, not guarantee it.
Be prepared to be surprised. Design more than one option and test them all. This also guards against two common foibles:
-Believing that you know more about suspension goemetry than the car's designer. Maybe so, maybe not...
-Believing that you know what the car needs. Surprises abound...
Keep your mind open. Spacers, offset bushings, parts swapping, machining, moving inner pickup points, allowed tolerances, and fabrication may be among the options for revising the production geometry. Study the rules carefully.
Keep in mind that your changes should ideally be either high-confidence or reversible. It's a big plus to be able to A-B-A test them, too. If the changes require major fabrication or machining, or are irreversible, then they must be high-confidence as well.
Consider a simplified or partial version of the expected direction. For example, maybe it's an easy job to move the roll center 0.50", but a hard one to move it 1.00". But you want to move it 1.00", don't you? So, move it 0.50" and test that. If the car and driver like it, now there' s ample justification to try the more difficult second step. If not, much work and money was likely saved.
As always, geometry is just part of a total package. Be prepared to tune bars, springs, and shocks to optimize the car for the new geometry.
Good luck!
But then, today, I had a rush job to prepare some modifications to the geometry of a production-based race car. And, surprisingly, that project generated the theme for a new blog entry. So, here we go...
We'll conveniently assume that you have already measured the car (probably a whole blog post of its own) and that you are already up and running with kinematics software. Bill Mitchell is an old friend, and I've used his programs for years.
The starting point to the whole process is learning what changes the race series rules will allow.
If the rules allow modifying or replacing the spindle/upright, you are most of the way to a from-scratch design. The steering geometry will be yours to invent, as well as most of the instant center-related items like camber gain and static roll center location. The series rules on inner pickup points will mainly handicap the ability to design the desired anti-squat or anti-dive, and will likely effect roll center migration.
If you're stuck with using the original upright geometry (with or without a usually tight spec on allowed modifications), then the freedom to improve the goemetry is much more constrained.
So, here's the basic situation:
-You will never be able to get a geometry with optimized roll center location and movement, camber gain, anti- geometry, steering geometry, and spring/shock motion ratio. Give up on that notion.
-The series rules and the car's original geometry will limit your options.
-It's pretty common that a geometry modification that helps you reach one of your targets will hurt your ability to reach another.
So, it follows that the MOST important job is NOT necessarily the design itself. It is, instead, successfully figuring out what change is most important for your car. For example, is it more important to lower the roll center, increase the anti-dive, or reduce the camber gain? Having decided what change is most important for your car, then it's time to review whether the almost-unavoidable tag-along changes will hurt the car, and understand how and how much they will hurt it. Finally, consistent with the theme of many of my posts, you will now hear me say that experience and education will only improve your chances of identifying what the car needs, not guarantee it.
Be prepared to be surprised. Design more than one option and test them all. This also guards against two common foibles:
-Believing that you know more about suspension goemetry than the car's designer. Maybe so, maybe not...
-Believing that you know what the car needs. Surprises abound...
Keep your mind open. Spacers, offset bushings, parts swapping, machining, moving inner pickup points, allowed tolerances, and fabrication may be among the options for revising the production geometry. Study the rules carefully.
Keep in mind that your changes should ideally be either high-confidence or reversible. It's a big plus to be able to A-B-A test them, too. If the changes require major fabrication or machining, or are irreversible, then they must be high-confidence as well.
Consider a simplified or partial version of the expected direction. For example, maybe it's an easy job to move the roll center 0.50", but a hard one to move it 1.00". But you want to move it 1.00", don't you? So, move it 0.50" and test that. If the car and driver like it, now there' s ample justification to try the more difficult second step. If not, much work and money was likely saved.
As always, geometry is just part of a total package. Be prepared to tune bars, springs, and shocks to optimize the car for the new geometry.
Good luck!
Sunday, September 13, 2009
I haven't forgotten you
Yes, I know the last new post was July 29. No, I absolutely HAVE NOT given up on the Race Engineer blog.
I have simply been covered up, in a major way, since late July. In today's business climate, that means, for me, multiple small jobs instead of one or two big ones. And, there's overhead associated with that. And, for you, an eventual blog post or two about how to get work, the new-job startup process, and juggling multiple clients.
There are also a number of new posts that are jelling in concept. Shortly, we'll commence two series, one on testing and one on setup sheets.
Hang in there, folks. Thanks for your understanding.
I have simply been covered up, in a major way, since late July. In today's business climate, that means, for me, multiple small jobs instead of one or two big ones. And, there's overhead associated with that. And, for you, an eventual blog post or two about how to get work, the new-job startup process, and juggling multiple clients.
There are also a number of new posts that are jelling in concept. Shortly, we'll commence two series, one on testing and one on setup sheets.
Hang in there, folks. Thanks for your understanding.
Wednesday, July 29, 2009
Philosophy, Vol. 1 Revisited
I'll touch on this subject one more time and then let it rest.
Just to show that our preconceived notions of what the racecar needs are often wrong, and that slavish devotion to simplistic notions of vehicle dynamics are equally wrong, it happened again this weekend at Autobahn.
One car I engineered felt like it needed a crisper turn-in with more support. But, it was worse with a slightly stiffer front bar, not better - as is often the case. Turns out it needed more low-speed bump damping and less front bar.
Another car I engineered lost front grip with a lower nose on the bump damping curve, despite expectations that it would gain front grip from that change. After all, the rear had just gained grip from a similar change.
At the next event, I may have to abandon these seemingly solid conclusions, too, if they prove to have been track-specific.
On my soapbox for the last time on this subject, for at least the next week:
-Listen to the car and the driver. They are reality. Your preconceived notions are not.
-The solution to a question may go contrary to common theory or your experience.
Just to show that our preconceived notions of what the racecar needs are often wrong, and that slavish devotion to simplistic notions of vehicle dynamics are equally wrong, it happened again this weekend at Autobahn.
One car I engineered felt like it needed a crisper turn-in with more support. But, it was worse with a slightly stiffer front bar, not better - as is often the case. Turns out it needed more low-speed bump damping and less front bar.
Another car I engineered lost front grip with a lower nose on the bump damping curve, despite expectations that it would gain front grip from that change. After all, the rear had just gained grip from a similar change.
At the next event, I may have to abandon these seemingly solid conclusions, too, if they prove to have been track-specific.
On my soapbox for the last time on this subject, for at least the next week:
-Listen to the car and the driver. They are reality. Your preconceived notions are not.
-The solution to a question may go contrary to common theory or your experience.
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