I don't run my PS2's on the track any more but I'm told you want them between 38 - 41 hot. It doesn't surprise me at all that you didn't show any measurable wear on your tires. 4 sessions isn't that much mileage and that track isn't terribly abusive on tires.

Think about the great value your car is giving you at the track and start booking your track dates for next season!