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Posted by: ken914 May 18 2006, 03:50 PM

I have my first Autocross coming up on Saturday and was wondering what air pressure is recommended as a starting point?

My car is a /6 with a 3.2, flares, roll stabilizers, delrin bushings, mono-balls in front, 245 Dunlop 8000's rear and 225 fronts.

Any thoughts will be appreciated!

Posted by: 1970 Neun vierzehn May 18 2006, 04:10 PM

Ken,
As I've AX'd w/a "4" on smaller tires than you are running, I'm not gonna recommend what will work best for you. However, as I've just returned this past week from Charleston, SC(wonderful city, as sure you're well aware), I'm wondering where your AX site will be. And whose running it? PCA? SCCA?
Anyway, have fun and be careful, as AX can be addictive!

Posted by: SirAndy May 18 2006, 04:21 PM

what does the manufacturer recommend for those tires for normal operation?

take that number and drop a few lbs, mark your tires and watch for sidewall flex.
less pressure usually gives you more "stick" until the sidewall starts to roll over. when that happens, you went to far and you need to pump it up a bit again ...

it's gonna be hit & miss before you find the best pressure for your tires ...

for your first AX, i wouldn't worry to much, leave them at your street settings if those are within the manufacturers specs and you generally like the way the car handles on the street ...

Andy

Posted by: Joseph Mills May 18 2006, 04:33 PM

I ran AX's with Dunlop 9000's, with 7" & 8" wheels, with 205's and 225's.

I started with 38# and kept dropping them down. At 30# the scuff marks were right on the edged of the face. They stuck great and I left them there.

I'm not familiar with your 8000's, but the 9000's have very stiff sidewalls. Very impressive street tire (although a bit pricey).

..

Posted by: jhadler May 18 2006, 04:36 PM

For your first autox, I would add around 10 psi over what you normally run. The side loads you get at an autox are considerably higher than what you get in regular street driving. A helpfull trick is to smear a couple dabs of white shoe polish on the shoulder of the tire where the sidewall meets the tread surface. This can give you a good idea of how much sidewall rollover you're getting. Less rollover is better, especially with street tires...

-Josh2

Posted by: turboman808 May 18 2006, 04:40 PM

Not sure if it's correct but I always went by my tire temperature.

Posted by: jhadler May 18 2006, 04:47 PM

Okay, sure. If you've got competition tires, and a pyrometer. If you're just showing up on streets for your very first autox, the first and foremost concern is to keep the sidewalls from rolling over to the edge of the rim...

-Josh2

Posted by: ken914 May 19 2006, 06:46 AM

Thanks everyone for your help!

Posted by: Dave_Darling May 19 2006, 11:38 AM

At the Zone 7 school, we typically suggest people pump their tires up to 36 PSI and then forget about them. The absolute last thing you want to be doing at your first autoX is to be fussing with the car. You're there to learn and have fun--and trying to figure out the course will take all the brainpower you can muster and then some!! (Trying to think through the adrenaline is very very difficult!)

For most reasonable wheel and tire setups, 36 PSI pretty much guarantees that you won't have the tire rolling over onto the sidewalls and then the rim. It won't generally be the best grip, but it should be OK. Sounds like, for these tires, 32 is probably also fine.

Pick a number, set the tires there the night before, and then forget about them. Concentrate on driving, not on messing with the car.

--DD

Posted by: jhadler May 19 2006, 11:39 AM

Well said DD!

-Josh2

Posted by: Joseph Mills May 19 2006, 12:34 PM

with Josh's agreement of DD's post.

Although I would set them at 34/36

..

Posted by: fitsbain May 19 2006, 01:32 PM

And old hand gave me some good advise the last time a raced the Camaro. I started with stock pressure I was running. Because of the limited slip and the wider rear tires it had a tendance to push into the corners. The solution was to raise the back tire presure. This helped the push quite a bit.

Lesson - You will end up adjusting pressures depending on how things perform.

Posted by: Joe Ricard May 19 2006, 01:54 PM

Sounds like a hot rod. Should be fun trying to control all that power on street tires. Just remember roll on the gas coming out of a corner like you are stepping on an egg.
Don't lift off the gas unless you are going to brake in a straightline.
Tail brake through the 1stpart of a trun and squeeze the gas through the last part of a turn.

Oh 38 to start cold and around 40 hot. White shoe polish goes just at the corner of the tread / side wall

Had a newbie put it all the way down to the rim. demo derby style.