This is a good resource for from miata.net that I didn't see referenced on the board. It will show you the differences in tire outside diameter, and a factor that you can use to figure out speedometer deviation with a different tire size. The only thing I wish the calculator did do would be show the speedometer deviation at multiple speeds. I'm more concerned with what the deviation would be at faster speeds like 84 miles per hour as indicated on the speedometer. Here are two examples using some simple math that use the factor provided in he calculator''s output: Say for example if you want to upsize a tire and the calculator tells you that your tire will cause the speedo to read 1% too slow. Multiply whatever speed would be traveling at by 1.01 to get the real speed. If the calculator were to say your speedo would read 1% too fast just subtract that 1 from 100 possible percent to get a factor of 0.99 or 99% and multiply that by whatever your traveling speed would be. http://www.miata.net/garage/tirecalc.html
thank you Offtopic a tad: Does anyone have a database of what cars uses what Bolt patterns and size and offset for stock wheels ? I moved a tad to the dark side and will be picking up a Honda Civic 2007 tomorrow and it has stock wheels and like to see what other OEM wheels will fit Bolt pattern is 114.3 but i dont know the Offset