Quote:
Originally Posted by The HACK
Stock tire/sizes are irrelevant. Outside of R-Comps most street tires will operate the best at around 38-42 PSI hot. Since autocross runs are never long enough to significantly heat up the tires, you need to shoot for at least 36 psi cold, especially in colder climates (I'd go as high as 38 psi cold if the temperature is below 60ºF, since it's unlikely you'll be able to put enough heat into the tires to increase the inflation pressure by 2 PSI).
Using the PSI and roll-over as a gauge will also improve your driving, because if you're significantly lower than the ideal pressure and you're not seeing any roll over, you can safely bet you've not used up all your available grip yet. If you're at the ideal pressure and you're still seeing significant roll over, you're overdriving the car and you're actually slower by unnecessarily sliding the car around.
Which isn't to say you need to push harder. It is but an indication that you've probably left some speed in the turns and the tires will likely continue to grip even if you enter some of the turns at higher speed. Usually what I do for our AX, is I start the day at 30 PSI only because we do our recon laps in the morning and they're back to back to back laps without any significant cool-down time (so tires will heat up like track sessions), but for the timed runs I pump the tires back up to 37 PSI and monitor the amount of roll-over/wear to see if I'm leaving traction on the table or over-driving the car, since the tires do cool down between runs.
Of course, this is assuming that your car is aligned with some camber in the front. If you're on stock camber then the rule is altered a little, since your ultimate grip is less with less camber.
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And to monitor roll-over, best to do is mark up your tires!
I use Chalk...cheap and not messy. I have yellow, blue, pink and green...
