Miata calculator is inaccurate
I was surprised to see that the Miata calculator is not accurate. It assumes that there is no tire compression under the weight of the vehicle. The actual revs/mi would be more than what they show due to this compression when the tire is in use. You can see the error by comparing, for example, what Michelin says the revs/mi are for a Pilot Exalto A/S 215/60, which is 800, to what the calulator says, which is 771. That's a significant error, about 3.6%.I made an Excel file that may help you wade through the myriad tire options
P.S. - An excellent tool for in-depth and visual comparison of different tire sizes is the...Miata.net Tire Calculator[/url]. There is a Java version and a link to the older non-Java version for those without the Java JRE. Give it a try!