BFGoodrich Mud Terrain KM2. I got 51,000 miles from my first set, and that was without keeping the truck aligned and the tires rotated as often as I should have. The two on the side that the truck was pulling to were worn out...the two on the other side easily had 5,000 miles left in them.

My second set has right at 3,000 miles and they are doing great.

LOL @ 40,000 from the Duratracs.