Tire pressures

[SGT2666]

I'm going to be autocrossing this thursday and I'm not sure what i should be running for tire pressures. The reason I ask is because I'm running 20's and I'm afraid of rolling a side wall and damaging a wheel. I've been running the recommended tire pressures from Ford and I don't really know if thats correct or not. Hoping one of the experts here might know the answer.

[LuLu]

I'm going to be autocrossing this thursday and I'm not sure what i should be running for tire pressures. The reason I ask is because I'm running 20's and I'm afraid of rolling a side wall and damaging a wheel. I've been running the recommended tire pressures from Ford and I don't really know if thats correct or not. Hoping one of the experts here might know the answer.

If I were you, I would start with -5 PSI from the maximum PSI as stated on the sidewall of the tire, and work down from there. -5 PSI will make the tire very hard, but the "slip and slide" factor will depend on track and local atmospheric conditions. Go high and adjust down to where you feel you're getting the best adhesion. I would not follow Ford's advice, they didn't make the tire.

 

Have fun, be safe, let us know how you did?

[mciarochi]

Here's an excellent thread. [Warning: Tire pressures are not as straightforward as you think, you can spend a lot of time chasing down the correct answer!]

 

http://www.teamshelby.com/forums/index.php...st&p=460068

 

In a nutshell, the 35psi (for the GT500) in the front and rear does not make sense. The rears are more lightly loaded, especially in the GT500, but also in the SGT. For the same contact surface front and rear, the tire pressures need to be balanced.

 

My GT500 has 15,000 miles, and after meticulously keeping 35psi in all four, I have significant tread loss in the middle of the rear tires, but like new at the edges. Classic overinflation pattern. The front tires are worn at the edges. Classic underinflation. Damn, so much for reading the owner's manual.

 

For the track, -5psi from the sidewall is a good start for the fronts. The rears should be proportionally less, depending on the weight ratio of your car. Even though it has less air pressure, the load on the tire is also less.

 

As far as the 20" tires, that's discussed in the thread above by a guy who knows a lot more than I do. You'll need to keep the pressure higher optimum. Because you can safely run a bit lower pressures, the 18's are considered by some to be better track tires for this reason.