Tuesday, August 30, 2011

Trackside Tuning - Who Wins?

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.

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.

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.

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:

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.

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!