I don't know if you have seen this:

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

It's a very nice tool to show graphically the difference in rims/tires cominations.

Quite easy to use too! Just put the stock specs in the left panel and the proposed sizes in the right.

Don't forget to use the correct offsets. All interference info is shown below. Instantly.

When you are finished you can save it to your favorites!

Best.