Tires & wheels
Automotive calculators that show their working
Tire sizes, gearing and engine numbers worked out from the formulas, with every step shown. Free, no sign-up, and they run in your browser.
Tires & wheels
All Tires & wheels calculators →What these are for
Changing tires, wheels or gears changes more than the look of a vehicle. Overall diameter moves the speedometer, the odometer and the engine rpm at cruising speed; wheel and tire width decide what fits under the fender. These calculators work those numbers out from the size codes and standard formulas, and each page shows the formula so you can check it.
They use nominal sizes. Real parts vary by maker and wear, so for anything that has to fit to a fraction of an inch, check the manufacturer’s spec sheet.