I have a friend that is running MTs in the back and ATs in the front. Hasn't hurt anything. The only thing is that if you want to keep the MTs in the back, you loose the ability to rotate the tires. If you don't care, then you can still rotate them. Either way it doesn't damage the vehicle any. When I bought my MTs I had 2 brand new tires and 2 fairly worn tires, but I went ahead and got all 4 MTs so that I could rotate my tires. I had 2 extra rims, so I put the 2 newest ones of the old tires on them so that I would have 2 full size spares instead of just 1.

Richard