not sure if you have seen this page or not, but it allows you to compare differant tire sizes. tells what rims they fit on. and then you can choose a few tires at this site to get comparisons. nice thing is that if you need a diff size for front and back, on the buy tires page you can pop both sizes in, and they will find you manufacturers who make both those sizes.

http://www.1010tires.com/tiresizecalculator.asp