[Mykl]

Originally Posted by T3h_Clap

damn, i used to run 49+ hot in the fronts to keep them from rolling over.

the rears would get to 45 or so.

tire chalk is your friend.

then again i had 255/40s on my stock 8" wheel so i need to compensate for the extra sidewall flex.

Tire chalk can be very misleading though, especially at the track. At an autocross where you don't get a whole lotta heat in them I suppose it can be useful.

But at the track with my RT615's my cold pressures have been between 31 psi to 33 psi, depending on the track, ambient temperature, and location of the tire on the car. Early in the session you're getting a bit of rollover, but when the tires warm up you don't get any.

[silver arrow]

I've found that 38 fr/ 36 rear cold is optimal for autocross. Less than 38 in front and the tires fold ( 245/45/17 on 17 x 8 ), more than 38 and I lose grip. The rears aren't as critical, you can play with them up or down a couple psi to balance the car. I run -3 deg camber front and -1.5 rear with 0 toe front and rear. Will be adding more caster soon and I will play with tire pressures again when I go to 8.5 or 9" wide rims.

[silver arrow]

Originally Posted by T3h_Clap

damn, i used to run 49+ hot in the fronts to keep them from rolling over.

the rears would get to 45 or so.

tire chalk is your friend.

then again i had 255/40s on my stock 8" wheel so i need to compensate for the extra sidewall flex.

Actually, a pyrometer is your friend.

[Turninconcepts.com]

There is no "right" tire pressure for those tires. There are WAY too many variables that go into determining the best pressures to run. Suspension setup, course setup, driving style all go into the pressures one should run. Some will prefer lower pressures and some higher. I tend to run on the low side of things, but that's me and my driving style.

[maxim05]

The best pressure I found with these at autox were:
35f/32r

No coilovers, no springs, stock camber with a WL front and rear sway at 29 and 24, respectively.
This limited the inital understeer and gave more neutral handling.

[T3h_Clap]

yea yea, i need a pyrometer.

[mx_9]

Originally Posted by maxim05

The best pressure I found with these at autox were:
35f/32r

No coilovers, no springs, stock camber with a WL front and rear sway at 29 and 24, respectively.
This limited the inital understeer and gave more neutral handling.

Same here. I ran them higher and had to bleed air out between runs because they were getting too hot. I now run about 31r/34f cold and the tires don't heat up nearly as much as with higher pressures. I've found that this pressure and being tuned to the tire noise and driving smarter when they squeal has brought my autoX times down.

[silver arrow]

I don't think those would work very well on a tight course, they really roll over under 38 fr for me and lose grip. Maybe you are running a different size than I am.

[blindfold]

what's a good street pressure when cold? 255/40/17

[smurfm3]

Originally Posted by blindfold

what's a good street pressure when cold? 255/40/17

I use the OEM pressures with great success. I have RT-615 in the same size. 36/30 works great. I used to run them at 38/34, then 36/32, but found a little too much understeer... so I dropped the rear a bit more. I like it because I'm getting better ride quality and more neutral handling. Even if they aren't as responsive as they would be at higher pressures, it is perfectly fine for the street. It ends up rising to 39/33 hot.

If I were going to go to an auto-x event I'd start them 3-4 pounds higher cold (40/34).