Speed Secrets: How To Best Use A Test Day - Part 2
By Ross Bentley
November 22, 2016
How did your test day go? Oh, that hasn't happened yet? Perfect. Because I have Part 2 of my thoughts on how best to use a designated test day.
Enjoy! – Ross
In last week’s article, I provided some overall strategy and key messages to keep in mind for your test day, as well as some that were specifically aimed at driver development. This week, we’ll look at car development.
A few key messages to keep in mind from last week that continue to be in play with car development are:
Make one change at a time, whether to your driving, or to the car
You need a (written) plan before you start
It's just as important to learn what doesn't work as it is to learn what does work
A change that improves your car or driving that isn't written down is likely to be forgotten, which means you're going to have to learn it again
Making a change that made an improvement, but without knowing why it worked is almost as bad as not finding any improvements
Now, to be clear, I am not an engineer. I’m not the best person to ask about how to tune your car’s handling. What I am is a driver who has had the good fortune to work with some fantastic engineers, team managers, and mechanics. And through the years, I’ve noticed some common themes and approaches among them. That’s what I’ll focus on here.
Speaking of fantastic engineers, Jeff Braun says to start the process of tuning your car by understanding what "tools" you have to work with. These tools are the ones in your real toolbox, but also what adjustments your car allows.
If the only tool you own is a tire pressure gauge, then adjusting pressures is what you'll work with. If the only components on your car that are adjustable are tire pressures and toe-in/toe-out, then that's all you'll work with.
Even if you have the largest toolbox in the paddock, and you can adjust tire pressures, alignment (toe, camber, castor), ride height, spring rates, shocks, aerodynamics... start with tire pressures.
It's important to take tire pressures immediately as you come off the track, having driven as quickly as possible on your "in" lap. Too many drivers do a slow cool-down lap, pull into the pits, then the paddock, slowly get out of the car, remove their safety gear, grab a drink of water, and finally check their tire pressures. Too late. Those pressures are not very accurate indicators of what's going on on the track.
I've heard people say, "Well, all four tires have cooled down equally, and it's the pressures relative to the other tires that’s important." Okay, it is the pressure relative to the other tires that is important, but there's no guarantee that the tires have cooled at the same rate. Whether one side or end of the car is in the sun when parked can make a difference. If the most important corner, from a handling perspective, is a right-hander, but the last two corners before the pit lane are left-handers, your pressure readings will not be accurate, even relative to the other tires.
As the saying goes, if the only tool you own is a hammer, everything begins to look like a nail. Thatʻs both good and bad. There's a limit to how you can affect the handling of your car using just tire pressures, but at least you're starting with the most important part of the car. Yes, never forget that everything you do, either with the car's setup or your driving, is transmitted to the track surface through your four tires. Get them as close to right before doing anything else.
Beyond starting with tire pressures, what changes do you make next? Alignment, springs, shocks, aero, or what? Again, follow Jeff’s advice and go with what you can adjust most easily. If tuning the shocks requires just the turn of a knob that’s easily accessible, then do that before changing ride height (since that will likely require much more work).
As part of your plan, make a list of all the things you can adjust on your car, from the easiest to the most difficult. While an experienced race engineer might approach these things in a slightly different order, when you’re at the track by yourself (or even with limited support), KISS.
Don't be afraid to make big changes. At the track, I'm often asked by a driver whether they should raise or lower their tire pressures, and most times I don't know because I don't know enough about the tire, the car, the track temperature and conditions, and a million other factors. So I suggest making any change - up or down - and seeing how the car reacts to get a direction. If raising the pressures helps, that's the right direction; and vice versa. But sometimes the driver will come back and say they couldn't feel the difference, so I'll ask how big a change they made. Too often, the answer is one or, at most, two psi. For a driver to be able to sense a change of one psi, they need to be fairly experienced, and be driving very close to the limits. The tire pressures also need to be close to ideal, so if they’re a ways off, you may not notice even three or four psi difference.
So, if making a change to tire pressures, don't be afraid to change them by five or more psi. Figure out which direction - raising or lowering them - is best, and then you can begin to home in on the ideal pressures by making smaller and smaller adjustments. But start with big ones to get a direction.
Doing "sweeps" is very important, no matter what part of the car you want to tune, because the first step is to learn what impact the adjustment has on the handling. By a "sweep," I mean start in the middle, go to one end of the adjustments, then to the other end, and make note of how the car responds at each point on the sweep. For example, with shocks you'd start with the setting in the middle, do some laps so you get a read on how the car reacts, then you'd go full stiff on that setting, do laps to read that change, set them to full soft, do laps to read that change, and make notes of how each felt. You will learn a lot by doing sweeps, and this applies to anti-roll bars, ride heights, camber, and so on.
Many people will immediately focus on tuning the car to make improvements to how it handles, and forget the main objective of learning. Given the opportunity to do sweeps, for example, I'd take that over making a series of small changes to chase just one handling problem. Doing sweeps will help you learn more in less time than making adjustments to sort out one problem. Think big picture and never forget why you're there: to learn.
How do you read what your car is doing well enough to know what to change, even if you have all the tools and adjustments in the world?
There's a process I recommend (if you haven’t downloaded the Handling Debrief infographic yet, do so now by clicking here). Instead of going into all the details, get a copy of the process. But for now, the number one thing you need to do is to ask yourself just one question: If I could have the car do just one thing better, what would it be? Once you answer that question, you can narrow in on the details by asking where on the track the car is doing what you don't want, where in the corner, and what you're doing with the controls when this happens.
Be prepared to feel like you’re going around in circles. After you dial in the perfect tire pressures, then work on alignment, or springs, anti-roll bars, shocks, ride height, and everything else, you may have to go back and tune your pressures again. One change can have an effect on other changes, and that means this is a constant evolution.
There's no way I can cover all the possible changes that you could make to your car in this article, but the principles apply whether you're adjusting tire pressures or the differential.
One last, very important point: When working as a test driver (and that’s what you are when testing your car and developing its setup), you have to drive consistently. If you adapt your driving to the car’s handling problem, you’ll never get the best setup. Drive consistently, and be honest. If you make a change, and you’re not sure you felt a difference, that’s okay. The worst thing you can do is pretend you felt something that you didn’t.
Finally, enjoy your test day. For many drivers, a test day is a very rare occurrence, so appreciate it. Prepare well for it, stay disciplined to your plan, focus on your driving or car setup (and not both at one time), make one change at a time, keep notes, use the tools you have to work with, drive consistently… and have fun!