I've put 31/10.50/15's on that body truck, they fill the wheel wells up nicely. You bhould get 15x8 wheels to use that size for the best perfomence. 32/11.50/15 will fit also, but they are a little tight. If you go to a 16" rim i'd suggest 245-75R16 or 255-70R16, they are the most common sizes in truck tires.
