Ok, I've got 40k on my BFG AT's. I've rotated them at least 4 times since i got them with 17k on them. The right rear drive tire is now on the front and looking a little thin. This has probably been discussed at length already but what if i criss-cross the tires if I'm just driving around town vs. highway speeds? I'd like to eek out a few more thousand before coughing up the grand for a set of tires.