Originally posted by PA 3L SVT:
OMG, I actually know this (I think). You apply chalk to the sidewall and tread of the tire (in a direction across the tread). Then, you can see how far down the tire has rolled during your run. If the chalk is worn down to the sidewall, you add more air to firm the tire up. If the chalk isn't worn to the end of the tread, you lower the air pressure to soften the tire up.
I usually put 4 stripes on.. and use shoe polish.. but yeah.. that's why we do it.
