Check out this tire/wheel size comparer

Check out this tire/wheel size comparer

there are tons of them out there on the web - but this seems to be one of the more comprehensive ones. Input OEM size (or it will find it for you) and desired upgrade size. Gives you all the basics - overall circumference, diameter, width, etc. etc. - nice diagram of the tire profile and dimensions - plus, it will let you know if it there are potential clearance issues. There are other factors that can affect clearance with tire/wheel packages that this cannot account for - but still pretty darn close.

Checked all of mine - where it said there would be clearance issues, I had them - the ones that should clear - yup, checks out on my rides.

http://www.rims-n-tires.com/rt_specs.jsp

Nice find....shows me exactly how big a tire I can stuff after the lift goes in.