Going autocrossing tomorrow with 18's, what tire pressure should I run? thx.

i did a little searching and it seems 42/40 would be good.

when i went auto-xing i found alot of different opinions.
 

some say that higher is better to support the stress of the vehicle shifting weight (what i belive is true)
others say less because the tire needs to flew, and the air needs to heat up inside to be a higher pressure tire.
your best bet is to go there with a grease pencil (other than the color black) and draw a line on the sidewall. then after each run see if the line is rubbing off. if it is you need more pressure because that means the tire is rolling over.
there is no way to keep it constant if you want the best performance. you will ge there and the tires will heat up and change the charecteristics.

good luck! and remember smoother=faster!

It depends, what tires are you running. You're going to have to experiment, but I usually run a
 

little more pressure in the rear tires. I'll often run about 38-40 in the front and 40-42 in the rear. Buffalo is right about checking how much your tires are rolling over, you can use chalk, shoe polish, or a greas pencil (I prefer the chalk, since it washes off easily). In all hoestly, if tomorrow is your first time out, you're probably going to have a hard enough time learning the course and knowing where to brake and turn to worry about your tire pressures.

Take this with a grain of salt though. I've only autocrossed the car 10 or 15 times in my life so I'm no expert, in fact, I suck.