AutoX n00b here... 1st time will be tomorrow.
I know i need to pump the tires up for this, however, i was just wondering...

The tire says DO NOT Inflate more than 40 PSI. Soo, if i were to inflate to 40 PSI, after driving for a bit the tires would get hot and the air would expand making it higher than 40 PSI.

This is ok right? Because they mean 40 PSI is the max when COLD, but they allow a certain tolerance and take into account that the tire will get hot. Right?

Hope it makes sense. I'm kinda rambling. I plan to put the Rear Tires at 40 PSI, which is 5 PSI above the recomended, and the front tires at 38 or so.

Any advice?

 

i usually run:

37PSI Front
34PSI Rear

As a matter of fact if the rain holds off i'm autox today ^_^

 

wow, we are taking about Auto Crossing, right? You know... stadium parking lot, cones, turning.

I kno in FWD cars they say pump up the fronts more than the rears to slighlty help with understeer. In RWD it was other way around in every respect.

Also, as a standard the tires on my car are to be inflated at 35 PSI. So i def need to go above that.

When i go to the 1/4 mile DRAG strip hower, i usually reduce the pressure in my rear by some amount.

 

FWD cars are nose -heavy and do need more pressure up front. I am with Glex on recommendation.
You can always change it...

 

Yeah, I'm a little late on this one but I'll chime in.

When My tires were 'new' the best setup for me was 47.5 Front & 37 Rear (HOT). That was with the RE050A. Took me all season and a stick of chalk to figure that one out. (NOTE: All tires, cars, and driver skill will produce different results)

Now that my tires are bald (Technically street legal, but at 1st glance they look like slicks). It doesn't matter whats in the front as long as it's above 45 and the rear is still 37 (they still have some tread).


Yes, the 40psi would indicate cold pressure. Actually you may want to take another look at that because performance tires should be able to go much higher. That may just be the mounting pressure.

Now here's what I've been told to do. Now look at your side wall just to the point where the actuall tread stops and go around the tire until you see a small carrot '^' that points AWAY from the rim. Get a crayon, peice of chalk, shoe polish, or something to make a noticable mark on the side wall of your tire. Mark the rubber from the center of the tread, over that carrot, and down to the lettering (i.e. company logo) of the side wall. Fill those tires up to max and run a lap. The chalk should be worn down to the tip of the carrot. If it's past the carrot you need more air (i.e. tire is flexing too much at the center of the contact patch) if that chalk hasn't been worn down to the carrot you need less air (i.e. the tire isn't touching the road at the sides of the contact patch).

Now thats a coarse way to adjust pressure and worked well for me this season. But for better results get a pyrometer with a probe. That way if you got the money you can fine tune your alignment as well (you'll have a temperature profile ACROSS the contact patch). I'm going to go that route next season.

I wish I could show you pictures but my computer and car are currently 1600 miles away . If I remember I'll snap some pics tomorrow at the auto show. The rental Mustang I got right now has some super high-life rubber with 640 wear rating and they don't have the arrows so I can't show you that either.

EDIT: Most of what is said here applies to performance tires, all-seasons and summers. But like on my mustang it's a crap-shoot for econo-tires. Best bet is to do yourself and the car a service. Thorw those away and get some Ultra-High performance or better tires.

-G
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Almost forgot. THis is what I was talking aboot.

 

Hey Gavin, great right up! (Sorry to bring this thread back to life 4 months later ... still researching tires and brakes for autox/track and ran across this)

 

The RE050A's are excellent AutoX tires if the club has a street tire class. The SCCA events do not however. And street tires (in theory) can't compete against a slick. I came oh so close to beating a 300ZX with slicks on last year my raw time was better but I hit a cone right at the end. Cheesed me off something fierce.

I still need to pick me up a pyrometer, especially now that I've been approved to solo for High Performance Driving Events (HPDE). I Don't have the RE050A's anymore I've "upgraded" to RE01R's on the front and PS2's on the rear. I found a good cold pressure for the front (wrote it down somewhere) but still working on the rear. I get a lot (...well... not A LOT per-say but more then I think I should) of roll-over onto the side wall. But that may be appropriate because of the different brands.

Also, it's better to go to a HPDE with a cold pressure about 5psi over the CAR recommended pressure (i.e. what it says inside the door). The track will heat up your tires much more then a single lap on an autocross course.