[little.one.der]

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

You should check it out. Covers every aspect all in one and you can even view the comparisons with or without either the wheel or the rim.

Hope it's not a repost.

 

[frictionfighter]

pretty dope, i hope it help people understand offset.

 

[jdmeg2]

it wont let me put a 195/50/15 on a 15x8 wheel..... its sux

 

[j0oftheworld]

That thing is pretty fancy!
The only issue I see with it would be "actual" tire sizes.. since tire heights/ profiles/ overall widths are usually dif.

Here's the one I always use.. down and dirty!
http://marksink.com/tire_wheel_offset/offset.html