When are DR's used up?
 

At what point do you consider a set of DR's to be "used up" and get a new set? I see they have a ridge in the tread that is like a wear mark and i was wondering how far do you let them go? Do you run them till theres no tread left and they are a slick? Or when they hit the wear mark? Do they hook any less after they are worn down? Ive only had mine half a season and id like to get the most out of them, but it looks like im only gonna get 1 season per set of DR's. -Jon

Are you ONLY using them at the track, on dry pavement?

Driving them to the track, then a dozen runs at the track, and then back home. -Jon