So I used to run on 265/40R18 tires for autocross, but I've made the jump to 285/30R18 this year. The pressures that I ran for racing on the smaller tires were 36 psi front, 34 psi rear. I found those pressures to give me the traction that worked best for me. My question is should I run those same psi's on my wider and shorter tires, or should I run a different pressure? Thanks

 

So I did some research on the SCCA forums and found that some people are running 42psi front and 36 psi rear. When I tried the pressures I found out that the front psi was way too high. I had major under-steer and I couldn't get any traction to save my life. I lowered the front psi to 38 and the car started handling like it should. Next race I'll try my old pressures to see if I get any more traction. Moral of the story, higher pressures tend to create lots of under steer.

 

It is really dependent upon the tire. Last year we had three S197's competing locally in RTR. Several different brand tires over the season. Tire pressures were anywhere between 32/30 and 46/42. Otherwise pretty much same cars.

 

That is a good point. I'm running the Dunlop Direzza ZII's this year. For the last two seasons I ran the Yokohama ADVAN Neova AD08. So both were extreme summer tires.