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

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.

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.

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