As I'm gearing up to start autocrossing this month, I'm wondering about tire pressures. Currently, on my Fd I have the stock twin setup, but with the Profec boost controller the 10PSI hits really hard and causes some driveability issues - i.e. it's easy to lose traction. What pressures f/r should I run for autocross? I have 225/40 F and 255/35 R Pirellis. I was thinking that I needed more pressure for better response, but I'm looking for a good 'rule of thumb' or something as a starting point for tweaking around with.

 

do the chalk pressure test...

refer to this post

 

I'm not too sure that'll help a lot since my tires are so low profile. I suppose I'll just follow the advice in the thread and try a 30PSI F/R setting and go from there.

I guess I can always just take the car to the nearest bigass parking lot and see what happens.

 

At the AutoX yesterday, I was told that most RWD cars put less PSI in the rear tires, and more up front. Both front and rear being UNDER factory max limit (written on the tires).



Yesterday, on Victoracers with Stock rims, I ran 38psi up front and 34psi on the rear.



Sidewall rolling will depend on air but also the tire make, Victoracers (r-compound) are very stiff. Mine were great! Not much to compare it to, though, than the street use I get off my Bridgestone S02's and short ride on Khumo Ecsta Supra's (too soft!) which it obviously surpasses.



Don't forget as you heat up the tires and get busy the air expands, you have to leave room for that. But the rule of thumb is less in the back than the front and adjust accordingly, all under factory limit.

 

I was told to bump mine up 10 psi from usual, to minimize tire wear. But I guess that's more of a "save your street tires" thing than a "maximum grip" thing.

 

[quote name='Baldy' date='Apr 18 2005, 01:07 PM']I was told to bump mine up 10 psi from usual, to minimize tire wear. But I guess that's more of a "save your street tires" thing than a "maximum grip" thing.


[/quote]



Yea, if you run the tire's "lower" there's more tread touching the ground in all instances/sitautions, so you get more grip and you have room for expansion when the tires get hot and the air expands.



Run the tire's "higher" and they'll stand taller, get a longer "reach" for better mileage and less wear.



I keep my Integra's tires near max, and the FD as stated above, more in the front than the rear, and never to the max psi.

 

Hard to give a rule of thumb on this question as there are WAY too many variables to consider (tires, profile, alignment, suspension and surface condition all change needed pressures).

I can run 2 different lots day after each and still need to retune the car for each different lot. I compete with 225-50-15 on my FC and usually start with fronts at 28 and rears at 24.