Awesome Tire Size Calculator
 

It even shows the view of the rim and tire

with 2 views. One with the current and one with what you want to try.
You can also find the size you want by available brands.
Check it out. It's pretty cool.

http://www.wheelsmaster.com/rt_specs.jsp

:favorites13:

agghhh it wont let me choose specs i want to see. =(

haha me either lolz

I use the miata sites calculator regularly. Stickied.

Try this one, then
 

'K den try dis one....
can't get too way outa da box you know.... :>)

http://www.discounttiredirect.com/di...foTireMath.jsp

compares 2 different setups and it's purdy kewl.

Awesome guys.