http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=53Once you determine the size or hight you want, just choose a tire in that size, check the spec's, and you will see the recommended rim size. Most tires will fit rims with a 2" difference, something like 6"-8" width. What you want to watch out for is the weight range of each tire. It helps to know the weight of the truck, and the split weight front to back.
On my '37 I run 205/75R15 on a 15x4 rim on front, 235/75R15 on a 15x7 on the rear. Mine weighs 3100lbs and is split almost 50/50 front to rear.
Joe
