When are these tires worn out? I have been told they are good for 6 races but is that a whole 28 lap night of racing (5 hot lap 8 heat 15 feature). My tires have anywhere from 3 to 4 nights of racing on them and from 26 to 98 laps total on them. What about tread depth? I have 6 tires and the tread depth rages from .098 to .128. I grind my tires before I race on them for the night. They still seem fairly soft but I haven't ground them again yet.