I just got an 07 XL 4.2L. I really want to upgrade the stock wheels and put the biggest tires on that will fit under a leveling kit. When I went to the local offroad shop, the clerk told me I could fit 315x70x17s on an 8" wheel but he said that I would probably run into power issues. What is the largest tire I could go with without have "power issues" and is there anything I could do to remedy the "power issues" without killing the factory warranty.

I have decided on 17"x8" Moto Metal 950s with either 315x70x17 BFG ATs, 285x70x17 Mickey Thompson Baja Radial ATZs, or either 295x70x17 or 305x70x17 Nitto Terra Grapplers.

PLEASE HELP

 

To fix your "power issues" you need to re gear.

 

All of the sizes would be "livable" with except the 315/75R17's (and of course, that's all preference). You'd definately want to regear with those taller tires... 4.56's.

 

I'd go lower than 4.56 gears with a V6. 35's and 4.56 gears is a good combo on a V8.

 

My truck has a hard time with 315's with the 5.4 and 3.73 gear's. With the 4.2 and stock gear's a 285 may even be too large. With the 4.2 engine you would need as low as 4.88 gear's to turn the 315's and then new pad's and rotor's to help stop them! Just my 2 cent's.

 

My last truck was an extended cab with the 4.2 it didn't like it when I put 32" tires on it. It couldn't climb a bridge on the interstate without kicking out of overdrive. I re geared to 4:10's and it and I was much happier.

 

I have a 4.2L V6 stock tires it was a bit of a dog, now I am running 35s with 4.56s and love it, I pass V8s all the time going up grades on the freeway also has a great hole shot.
You will also need to recal. the spedo at a dealer or buy a programmer...