Stock tires, right?
In general, you want to set the FRONT tires so that they don't roll over onto the sidewalls in turns. To do that, you'll need a pretty high pressure (I used 45+ on the stock Yokos on my Celica when I got it...) and you'll want some chalk or white shoe polish. I'll explain the procedure below:
1.) set your tires to a beginning value. (I recommend 40-45psi)
2.) Mark on the edges of the tread and over onto the sidewalls with the chalk or polish. Mark it so you can tell after a run how far over the edge of the tread onto the sidewal your cornering forces have rolled the tires.
3.) Go run!!!
4.) After the run, look at how far down the sidewall the polish has been worn off. Ideally, the edge of the polish will be right at the outermost edge of the tire tread blocks.
5.) If the tire rolled over too much, raise the pressure 1-2 psi and try again. If the wear did not reach the edge of the tread, then reduce pressure and try again.
All of the above applied mostly to the FRONT tires on a FWD car. Now the hard part: the REAR tires.
6.) Once you have the front pressures set right, then set the rears. What you want here is to set the rears so they have the right amount of grip to give the car the handling characteristics you want (i.e. how neutral, understeering or oversteering you want.) Start with the rears at the SAME pressure as the fronts. Then take on of two options: raise or lower the rear pressure to get the car to rotate how you like. In the vast majority of FWD cars, equal pressure front and rear will cause understeer. By adjusting the rear pressure, you can adjust the balance of the car. This is an ART, not a SCIENCE and there is no set way to do it: it's all up to choice. In general, though, the larger the difference (in either way) between front and rear pressures, you will tend to see more oversteer. The rear end will tend to rotate better (or too much.)
When my last car was stock, I ran 45psi in front and 26-28 psi in the back to get the car to rotate more. I have seen other people get the same results with 45 psi F and over 55 psi rear. It's all up to you and your preference.
My advice would be to find someone experienced at the next event and latch on. Ask questions, get advice and learn how tofigure ot your own best setup yourself. AS you get experience, it will get easier, but not easy.
BTW, a better way to set the front pressures would be to use a pyrometer and measure the tire temp on the tire on the OUTSIDE in the LAST corner of the run IMMEDIATELY when you get back to staging. The perfect pressure for the tires is the one where the tire temperature is EVEN all the way across the tread. Riase pressure to get higher temps in the moddle, lower pressure for higher temps at the edges. Be careful, though: camber and toe play a role here: If you have little negative camber (the tires look like "I I" or even "\ /" from the front) then you will have higher temps at the outside edges no matter what you do....
But how many beginners have a pyrometer sitting around? I don't after several years.....
Have fun, make friends and have fun.....
