Thanks to our friends at Miata.net, We've secured this customized tire size calculator for you to compare your current tire size to a new and different size tire, or any two tire sizes you might think of (well, within reason).
Please note that this requires a Java-enabled Browser
Once again, thanks to Gary Fischman for the Java Applet, and customizing it for Turbo! Thanks also to Miata.net where I found Gary's calculator.