There is a way to run a 15 or 16''.. It just looks very odd.. I've done it. Run a wheel with only a few inches or less backspacing. It sticks the tire way out but it works. Real Racing Wheels built the set I was using. Then I had to stick them back on the truck they were made for. Have you went to Rancho adjustable shocks yet? They help free the rear of the truck up. Also run with your spare tire and hitch on the truck for added weight where you need it. I'm about to start adding more weight to the rear of mine..