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FD autox tire pressure

Old 10-01-08, 09:04 AM
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FD autox tire pressure

My first autox I ran 5lbs extra per tire. I have my second event coming up. Too much?To little? What are you more seasoned guys running?

It's a pretty basic question and may have been covered but I'm on the crapper at work with my iPhone and it hard to search

Thank you.
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Old 10-01-08, 01:26 PM
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What kind of tires? What sort of suspension and alignment are you running?

Very generally speaking, you want to maximize your grip by running the lowest pressure that doesn't cause sidewall flex and tire rollover. To that effect you can mark the sidewalls of your tires before your run with windshield chalk and see how much gets scrubbed off during the run. Also, be aware of the change in tire pressure due to tires getting heated up by measuring at the end of each run. Also, if the course you're running that day is more right or left-turn biased, you'll probably end up adjusting the tires differently as the outsides will heat up faster and more than the insides.
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Old 10-01-08, 05:02 PM
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wow, i didnt really think it through like that. i was told to run higher pressure at autox as to not roll a bead.

theyre street summer performance tires 245 wide on 17x9 rim. eibachs with normal alignment

normally they are 32 front, 30 rear. im still exploring the limits of the car.
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Old 10-01-08, 08:36 PM
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I've seen street tires at street pressures be pushed way over so that the shoulder is rubbing the pavement - not good. So they tell new autocrossers to up the pressure 5 or 10psi because the average car tire is not stiff enough in the sidewalls. It's a safe approach. But many good street tires perform better with closer to normal pressure.

At 32lb my RE-01R's are nowhere close to running off the tread surface. When I run my v710s I run between 27 and 29lb.

Mark the tires and see exactly how far you're getting off the tread surface. Your tires probably have a small arrow or mark to indicate the farthest they are designed to touch the road. If you exceed the mark add pressure. If there is no mark, it's usually pretty easy to judge where the full thickness of tire tread starts tapering down toward the shoulder section of the tire and use that as your guideline.

Not trying to bust your *****, but you've done one event you're not going to be exploring the limits of the car for quite a while. So I'd pay attention to how your tires are contacting the pavement, and use that to pick a sensible tire pressure and leave it there. Bleed down the tires between runs to maintain that pressure. I believe in keeping things constant so that I can provide the purest feedback for my development as a driver.

Dave
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Old 10-02-08, 01:44 AM
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Originally Posted by dgeesaman View Post
I
At 32lb my RE-01R's are nowhere close to running off the tread surface. When I run my v710s I run between 27 and 29lb.
I'm running 285/30/18 V710s in the same range.

Started off with 35psi - it was terrible - no grip.

But then again, a 285/30 has a very low stiff sidewall, and doesn't roll on the shoulder as easily as taller and narrower tires.

So the answer is "it depends".
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Old 10-02-08, 05:10 PM
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Originally Posted by dgeesaman View Post
Not trying to bust your *****, but you've done one event you're not going to be exploring the limits of the car for quite a while.
Dave
i have no delusions about my driving skills...they are not very high

im very much a novice and maybe i should of phrased that comment differently to get my point across. im still learning to become a better driver and drive the 7 to the limits.

arent you from Harrisburg? this is what im doing as my second autox: http://www.greaterreadingautoexpo.com/ thats not that far looking for a protege? im a sponge

everyones comments were helpful, thank you.

i have all the bolt ons except a high flow cat. im running a pfc, eibachs, and strut brace @ stock boost, they put me in SM2 at my first autox, that sound right?
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Old 10-02-08, 05:18 PM
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Most "bolt on" mods are legal for A Street Prepared. You said you were stock boost so I am assuming you are still the stock twins. When you start changing turbo components or internal porting of the engine you get bumped to Street Mod 2.

The entire rule book is free online at SCCA.com:
http://scca.com/contentpage.aspx?content=61
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Old 10-04-08, 08:42 AM
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The radiator is one component that bumps a lot of FDs out of ASP and into SM2.

As of next year it will be legal in ASP if it's not smaller/lighter than the stock radiator.

That event in Reading sounds good. I'll try to check my schedule and register today. Bugger I was out traveling for work and missed the advanced registration deadline.

Dave
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Old 10-04-08, 03:46 PM
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Originally Posted by jkstill View Post
I'm running 285/30/18 V710s in the same range.

Started off with 35psi - it was terrible - no grip.

But then again, a 285/30 has a very low stiff sidewall, and doesn't roll on the shoulder as easily as taller and narrower tires.

So the answer is "it depends".
That is a wide, flat tire.

Even if your tire pressure is about right, you definitely need to get your camber and roll stiffness set up to put that patch flat on the pavement. The stock tires and wheels are much more forgiving about it.

Dave
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