It just depends. You can easily fit a 35x12.5 tire with a 4" suspension lift, but you wouldn't have tons of room. Something in the 33-34" range (maybe a 285/75/16 or 315/75/16 if you want something wider). I assume your running stock wheels now? Why is negative out of the question? The larger (wider) your tire gets, the closer it's going to be to the frame and everything else inside when you turn. I'm here to tell you that your going want to have a wheel with a MINIMUM of 0 offset. Personally I would run something in the -6 to -11 offset range. First, it would push the tires out just a bit AND more importantly it would give you clearance on when you turn.