Using chalk to determine tire pressure Options

[ChrisReale]

On some tires, there is a triangle on the side wall by the tread that you can use to determine how much roll the tire is experiencing. How do you use chalk to mark the triangle to determine roll? I am curious also about Victoracer tire pressures. I started out at 30psi, but determined the car handles better at 26 or 27 psi. This seems a little low to me. Any comments?

[VegasRacer]

Just put a 3" line across the tread and up the sidewall. I use white shoe polish. After a run session you can see how much roll you were getting by where the line is rubbed off. Aboooooout ....... there is perfect. Judge your tire pressures by what they are at the end of a session. 26 - 27 is not to low to start. I put 2 less in the front outside tire. Maybe 1 less in the outside rear (depending on the track). Mine feels good when I come in with hot tires at 30 - 31. If it gets much higher the Kumhos feel slippery. 30 would be an OK start if you are just autocrossing since the tires will never get a chance to heat up. Play around with it. What ever feels good (and produces lower lap times) is the right number. You optimum start pressure may change depending on the ambient temperature and the track surface.

You can get better information if you have a pyrometer. (I don't have one) I see all the fast/expensive racers do. They take inside/center/outside readings on each tire. I don't know how they interpret the data. If somebody else post a reply, we can both learn something.

[Don Wohlfarth]

Using the triangle on the sidewall of the tire you adjust pressure so there is a scuff mark to the edge of the tire from the track surface. You want to adjust pressure until you barely touch the tip of the triangle. This method works well until you start running +2 or +3 tires sizes over the oem size tire. Lighter cars don't have enough weight to keep a flat foot print with oversized tires.
Using tire temps you measure inside, center, outside. Temps should be higher on the inside, to the outside. In a perfect world the temps would be even across the tire but that seldom happens. About the best you can hope for is about 15 degrees from inside to outside with inside being the highest. Temps are usually in the 160-200 range. I run Michelin Pilot Sport Cups 225-245 X 16 on my 1900# 914 and don't see much above 170-175 even on hot days.