i dont know if this has been posted before. but here it is:

http://mr2.com/FORMS/tire.html

 

Thanks, lcf. I think there are a few people who are aware of that calculator, but most prefer the one at:

http://www.miata.net/garage/tirecalc.html

That's probably because tje Miata.net calculator presents it's data in both written and graphical formats.