I just bought a 2007 gmc Z71 an had a 2 1/2 inch leveling kit put on the front an was wondering if some bfg all terrain 305/65/17 would fit or would I have to do some modifiying

 

I have a 2003 2500HD 4x4 all stock and I wondered the same thing when I bought it so I brought it my a local modafication shop and they informed me NO. They told me I could put 265s on it and if I didn't mind a little rubbing on the bumper from time to time I could go 285s. With a 2" leveling kit I would imagine you could go with the 285s without rubbing but I don't think you will make the 305s. Our front bumpers are just too close to the wheels.