I bought a 2003 XR650R a couple of months ago and unplugged it after about 20 miles. I ride primarily on trails but I also ride about 10% on paned roads. I try not to do a lot of heavy eccelerating while on the pavement but the back tire is wearing extremely fast. I have been shopping for a new tire and I'm leaning towards the pirelli MT21. Could anyone tell me how big I can go or if there are any better choices? Oh yeah most of the trails I ride are pretty sandy. Any info would be greatly appreciated.