Setting tire pressure settings?

[shenanigans]

any tips? I usually just run what feels right and look at the tire and eyball it.

any more "scientific ways?"

[Question]

A gauge?

[Wicked 3800 V6]

SERIOUSLY! [img]smile.gif[/img]

For me it's usually 40 up front and 28 out back.

[shenanigans]

well **** I thought it was known to use a guage...

I am saying that its at the right pressure, I normally run ~38 up front, and 40 in left rear ~36 in right rear.(Open diff)

[John_D.]

I've only run 18" street tires on mine.

I used chalk on the sidewalls to see how much scrub I got. I usually run around 38-39 front, 34-35 rear.

Most f-body guys say they run a lot less rear for power down out of corners.

I think the 18's are less prone to rollover. Plus you only get so much traction with a 245mm street tire anyway... [img]smile.gif[/img]

[Vracer111]

Originally posted by shenanigans:
well **** I thought it was known to use a guage...

I am saying that its at the right pressure, I normally run ~38 up front, and 40 in left rear ~36 in right rear.(Open diff)

Depends on your tires. I normally run ~35psi front and 32psi rear with the 275/40-17 Nitto NT-555RII's. And with the normal street 245/50-16 Yokohama AVS ES-100's I run about 40psi front and 32psi rear. Tire pressure really depends on weight of each end of the car - the end with more weight needs more psi, and that's usually at the front.

[shenanigans]

I understand some starting points, I am looking on tips on adjusting the pressurs after each run, I know slightly about the chalking method but not much.

just wondering if anyone had a good explanation for it.

[John_D.]

Basically you want enough pressure to keep the tire from rolling over, without so much pressure that it starts rounding out the tread patch.

Put 2 or 3 chalkmarks from the edge of the tread toward the center of the wheel. Then check after a run and see how far up on the sidewall the chalk got scrubbed off. You want about 1/4" or so to get scrubbed off.

That gets you in the ball park anyway. After that, it's just tweaking 1-2 psi to see where you get the best turn-in/rotation, and to dial in how well the rear grips on exiting the corners.

Some guys will measure the tire temps at outer, middle, and inner to see what's going on. Autocross may not really get them hot enough to do that though. And even then, some guys will say they had the temps just right and still corded the inner edge of the tire, so the temp method isn't perfect either. (I suspect those guys had excessive negative camber for their tire setup)

[FireFighter]

Dont run less in one rear even with an open diff because you will spin which ever one that doesn't have traction. Thats like getting on awsome track tire for one side and the other stock.

[zlexiss]

I agree with John D, use the chalk trick. Remember that ideal pressures are different for different cars with the same tires, and different tires for the same car.

I ran 38/30 with Falken Azenis Sports which have very stiff sidewalls, and run 44/34 on Kumho MX which are much softer in the sidewall (but just as sticky and much lighter)

Pyrometers are nice, and you can get good results even in autocrossing. The probes will work better than the laser ones. I usually borrow one when I'm on a new set of tires or if I make any suspension changes to tweak an ideal pressure, and then just memorize it and keep the tires there without chalking. Tire wear has been great and the car feels very consistent since I started doing this.

-Jeff