How do you determine the optimum tire pressures for your car? In other words how do you know when the tire is working "correctly"? I've seen the people with the shoe polish on the sidewalls. This is usually only at AutoX events how about HPDE etc.?

 

You kinda want to do the same thing. A little trick I did was use tire cleaner on my tires to get them nice and shiney (if you don't want to use shoe polish) and see how far the roll over goes by taking off the tire cleaner (shiney part). I think I was running 38psi all around.

 

If you have adjustable camber, the best way to do it is to use a pyrometer. You can then take tire temps across the tread (inside, middle, outside). It depends on who you talk to but usually you will want about a 10 degree spread with the hottest area being inside. If you don't have adjustable camber, the shoe polish works. Just keep adding pressure until it stops rolling over.

 

In a truly ideal world, you would have some idea of what tread temperature your tread rubber grips best at, and strive to achieve that operating temperature across the entire surface of the tire. Pressure and camber (and other alignment settings) are interactive so the only way to really get a handle on the variables is to test, changing one thing at a time, running, and then recording temps across the tire surface like civicrr described. It is possible that your best lap times might not be achieved where the rubber is working the best, however (due to car balance or driver preferences) so the stopwatch is an important tool as well!

I typically crayon the outside edges of tires on road race cars, to get a physical picture of how they are rolling and provide another piece of data to consider with the temperatures.

Once you get things figured out at operating temperatures, don't forget to let the tires cool down and note the "cold" pressues, so you will know where to start them in the morning the next time you come to the track, so you can get back to your optimum hot set-up. Temperature and pressure gain (cold to hot) will not be the same at all corners on a road course, since one tire is always working harder than the others. Keep records of all of your data!

Kirk

 

you can use chalk as well on the outside edges. Mark at least four different spots around the tire. Get some of the thick sidwalk chalk. This is a cheap method...the pyrometer is the best way though.