Yeah, chalk comes in pretty handy for that. It's also cool for seeing how far you roll over on the sidewall under extreme cornering. Even cooler than chalk though, is using a laser thermometer. I've seen dudes at autocrosses do that a couple of times. Basically, they do a few laps, and then check the temperature accross various parts of the tire.

Yeah, I guess that is a little out of control. But hey, those guys are sponsored.