We run both 21.5 TC and 13.5 TC foam classes... I run the 21.5 and love it. We are putting down laps just a couple of tenths off of the 17.5 rubber... with a tighter course, we are close to the same. I have been getting 3+ full race days out of a set of tires easily. I swap left to right and haven't had to true them. I do check and adjust droop and ride height as needed though. The last set came off with some white rim showing through... good enough for 3rd place in the A main... I hadn't bought new tires in over a month. If these new spec tires last longer and have about the same traction, then great!