[GMJimmy]

Thanks everyone for your input! It's very helpful. I have 275-60-15's on the back and have roughly 1.75 to 2.00 inches of space from the bed to the inside edge of the tire and about .75 inch from the outside of the tire to the inside lip of the fender until the suspension is compressed completely where the outside edge then rubs slightly on the inner part of the fender. Looks like I could use 1 inch more back spacing. These rally rims are 15X8 with a 4.25 inch back space. I was worried about lower control arm clearance with more back spacing but not with 17 or 18 inch wheels.

So those of you that are running 18 inch wheels, what tires are you using and what is the back spacing of your rims?
Thanks.
Jim