Recently purchaced a GMC 2500HD 4x4 crew cab.I want to put larger wheels and tires without having to lift my truck.Anyone know how big I can go without any rubbing?

285-75-16

Yep, what he said.....

You could throw some 33x12.50 hogs under that truck with out having to do anything. A 3 inch body lift which is fairly inexpensive and easy to install would probably afford some 35s without much trouble.

I have the exact same truck and I can run 285-75-16s and they barely rub the black rubber piece on the edge of the fender. Its easy to shave off. I also had to turn my torsion bars up a turn and a half. There is no way you can run 33's without them rubbing and not cranking your bars all the way up.