In autocross, time has way more to do with cornering than straight line.
Under extreme side load, the tread shifts more than in normal driving & footprint goes away unless the pressure is high.
Also a ~1 minute run won't heat up the tire much.

Most autocross drivers bring a small compressor to the event, pump up the pressure to run, then let it back to normal to drive home.

 

Thanks SureShot, for that in depth answer. I'm definately going to be trying this in 3 weeks (next autoX i can make).. I can't wait to try that, with my new tires, and my new tokico illuminas w/ Eibach Prokits.. . should be a nice improvement

 

I've ran my car at the race track (road coarse) a couple times, once with all season 15's and the other time with high performance 17's. For the best performance you want the tire to roll over just a little bit onto the shoulder (there will be arrows on the sidewall or on the side of the tread). The tire, when fully warmed up should roll over just to that point, and it'll be perfect. This is what the chalk is good for, it'll show you how far down the tire's rolled over. I've found that with the 17's 34psi cold was perfect, for the 15's it was about 34-36 cold. For street driving keep it at about 30-32 and you'll be fine. Also as others have stated, never put the maximum pressure in while the tires are cold! You shouldn't ever need to get the pressures up that much anyways, you're throwing away grip and shortening the life of the tire.

 

Cool, thanks Black91n/a, Maybe i'll have to bring some chalk next time I go.. .

There is lots of VERY good info in this thread


Just for the record, it was inflated to 30 PSI originally... I just got done tossing that cheap-*** gauge...

 

First time I've ever heard that air added weight. Can you explain this?

 

Air has a weight, just like any matter does. Whether that's enough added to be concerned about is highly debateable.. If you need proof, weigh an air tank empty, then fill it to 45 PSI or so, then weight it again..

I didn't say it would be a BIG difference, though

 

Yes air has weight, the more compressed it is, the heavier it is for a given area. Air weight isn't going to be very noticable.

I try to run around 35psi all the way around on the street. I can deal with the stiffer ride, and can really use the added gas mileage.

 

I'm currently running Toyo Proxes FZ4s. I tend towards "spirited" driving and autocross. I noticed that I had mild understeer at 38PSI and the front tires were scrubbed down into the sidewall a bit. Much of that problem went away when I went to 42PSI, although they still seem a little squishy. I'm mostly pissed about these tires cause the traction just went away after about 5000 miles.

 

Try the toyo t1s. I have them and they are awesome.