If you look at the front left tire in this pic:
you can see a little of what I'm talking about. In a turn, the car pushes outward and the tire tries to stick to the road. Something's gotta flex, right? The sidewall of the tire does some of that work. When it does, more of the sidewall winds up in contact with the pavement - this is "rolling over".
At the track, you typically take a piece of chalk and mark a couple of spots on the tire - rub the chalk on the shoulder of the tire. Then, when you come in, you see how much of the chalk mark is left. It lets you know what part of the sidewall touched the pavement.
I was wearing maybe .5cm lower than I really wanted to. The problem is that when the tire rolls over too much, it wears out the outside shoulder of the tire well before the rest of the tire, and you wind up having to throw the tires away before they are really "worn out" because the outside shoulder starts to cord (the metal part of the tire starts to poke through the rubber, and failure is going to happen soon).
these are the previous tires that came on the wheels I bought... these were corded on the outside shoulder:
