Solemn's Site
Never stopping to think if I should.
Speedo Error Calculator

This tool calculates the speedo error in a car when the tyre size, diff ratio and/or speedo drive ratio are changed. It can also provide the old speedo calibration and new calibration required to make it read correctly. Tyre sizes can be inputted in metric (i.e 235/85R16) or imperial (i.e 6.00x16) formats.

Tyre size:
Diff ratio: :1 :1
Speedo drive ratio: :1 :1 (If known)