285/645/18. What does the sidewall height of 645 relate to? Is it a 35/30/40 etc....? Thanks,
Jim

 

It's the overall diameter of the tire... race tires don't use that silly sidewall-as-percentage-of-width/aspect ratio garbage that street tires do.

It's millimeters, so divide by 25.4 to get the height in inches.

 

Thanks... on track soon I hope..