vacantskies88

Looking to run a Solo 2 Autocross event this weekend and I'm not sure what a good starting point would be for tire pressures. I've been running a nose-heavy front wheel drive VR6 GTI previously and would start off with 44F/38R. I am on the stock 16" AP1 wheels and stock 205/55 & 225/50 S-02s.

Thanks in advance

CobraTi

S-02's have stiff sidewalls, from my understanding. I'm on tires that I doubt are anywhere near as stiff and I normally don't adjust my tire pressures at all from the normal 32-33 I run on the street (will actually start to let air out once heat gets into them so by the time they cool down at the end of the day, they're down to 30psi or so).

My advice is to start at 35 all around, see how that goes, and adjust from there.

vacantskies88

Sweet, thanks

__redruM

Autocross is definately a handling test, so higher tire presures seem like a mistake. Not that I have played with tire presure at an autocross event, but I too would recomend 30psi or less.

KerryF

We have multiple nationally competitive drivers locally and I have been fairly competitive recently.

I run the same sizes and run 43 PSI all around. I wouldn't recommend anything lower than 40. If you look at the following picture you can see that I'm just rolling to the outside edge.



My alignment is:

Camber F/R: -1.6/-2.5
Toe F/R: 0/ 1/4"

WashabiS2K

you might be able to get better responses in the Racing and Competition section.

__redruM

Less presure = Bigger patch = better handling
More presure = Smaller Patch = less rolling friction, higher speeds

I'm not speak from actual experience here, so correct me if I'm wrong...

KerryF

That might be good for drag racing, but at autocross we take turns. Low pressure = rolling onto the side wall and reducing your usable contact patch.

Start around 40 and adjust from there. I used to run 225 Falken's on my BMW. At 34 PSI I didn't have any roll onto the side wall but I found out later that I was only running on the edge of the tire and barely using the middle. I bumped it up to 50 PSI and greatly improved the grip of the tires.

Street tires need high pressures, the story is different for Rs where you need to get heat into them.

CobraTi

Theoretically, less pressure the better. However with really tight turns, if you lower the pressures too much, you'll roll the tire over onto the sidewall or the car won't rotate, which is why its normally better to run slightly higher pressures. Plus, higher pressures let the tire heat up (ie get grippy) faster, which is very good when driving on courses that usually are less than a minute long.

GTI 20v

Why do people insist on posting even when they have no idea what they are talking about?

Your two best tools for choosing tire pressures are chalk/shoe polish and a pyrometer. Put the chalk on the edge of the tire tread and sidewall. This gives you an indication when the tire is rolling over onto the sidewall.

Second, use a pyrometer to measure tread temperatures across the tread face. Ideally, you want the temperature to be the same on the inside edge, center, and outside edge. If the edges are hotter than the center, raise the pressure. If the center is hotter than the edges, drop the pressure.

40 psi as suggested above sounds like a great starting point, but your pressures may differ based on the course surface, outside temperature, and whether the course is wet or dry. So start at 40 and adjust from there. If at 40 you are not getting any sidewall roll, drop a few psi and try again.