I was at an auto X 2 days ago and was wondering about tire pressures. In the morning on cold tires I was running 34/35 F/R on my 235/40/18 Eagle F1 GS-D3's. Once they got warmed up they were at 35/37 F/R. I was getting alot of Push/Understeer so I lowered the tire pressures to 32 all the way around. I immediatly shaved 3 sec off of my time. This is kind of counter intuitive though since most people reccommend running higher tire pressures. What is a good tire pressure to run at? I am stock exhaust for an exhaust and the Eagle F1's Is there a place/site that has some type of general reccomendations for various tire pressures?

 

https://www.rx8club.com/far-east-asia-38/recommended-tyre-pressure-90948/

My owners manual says:

for both Front/Rear

32psi

I hope that helps.

 

32 all around.

 

there should be at least a couple of threads on this topic over on the Comp forum. basically, you want to have your pressures high enough that your tires (usu. the fronts) are not rolling over onto the sidewalls from hard cornering. that's why people usually take some white shoe polish or wax pencil and make markings on your tire edges before AutoX runs, and see how much roll-over you're getting at a particular pressure. once you have enough front pressure, you then play with rear pressure to tweak the balance of the car.

depending on the tire construction/design, it might be possible to get best grip with the tire rolling over somewhat...but, it may also lead to an early grave for your tire. some folks also prefer giving up a bit less absolute grip by pumping up the pressures, but in return you get a bit crisper steering response (turn-in).

FWIW, on my all-stock car (except for alignment), I've settled on around 38 psi for the Fronts.
*EDIT* the above is assuming AutoX event, which is what I think you're interested in. I run 34 psi cold on the street.

 

So that's why they use the shoe polish. It's kind of weird. I have done maybe 10 AutoX and never once thought of asking what thoose people were doing. I will try that out at the next event and see how the car feels at differnt pressures. Thanx

 

Jerry,
Usually you would start at +5psi over the recommended pressures and adjust from there. Using the shoe polish is a great way to tell how much tire roll you are getting. You want some roll, but not too much. As for your 3 second time increase, I don't think you can attribute that to a small change in tire pressures. That was mostly you learning the course and maybe slowing more for those corners that you were pushing badly.

Talk later,