I have an 1984 K5 with 35 X 12.5 X 15 Cooper STT's. Im using a 15 X 8 rim so that I can air down more without popping a bead. The 15 X 8 rims keep the tires more inside the fenders, so a wheel that is offset different will give different results. Some people use 15 X 10's but I like the 15 X 8 set up better. If you go wider, then the front will catch the front fender at full turn and full flex.My truck is a 1987 chevrolet with a 4 inch lift and 33 inch tires. Whats the biggest size tire I can get in there with out any problems?