[501X Driver]

Our track is hard pack with a little dust on it and they keep it moist. Good Traction, a matter of fact I can't keep it from traction rolling unless I slow down in the turns, and who really wants to do that. And when I say slow down I mean more then you should need to slow down, I do not try to take a 90 degree corner at full throttle. The corner even has some banking in it.
I used the factory belt and pulleys (16T,35,36) for 5 months running every weekend with no problem, we changed the track and it had some loose dirt and I tore up 2 belts and a cuple of rear pulleys. I have purchased 2 sets of the covers. But once the track was back to normal no problems, I run my rear belt a little loose then I think it should be and the front about the same as the rear. You can pull them up about 1/8"-3/16", 1/4" seems too loose. I have run 4.5L and now a 5.5R.
Your front belt last longer because when you are putting the power down the weight transfer to the rear and the front tire will slip, so most (probably 80%) of your drive is the rear tires.