Tyre size
Enter your numbers — the results update instantly.
Worked example
Given: Width (mm) = 205; Aspect ratio (%) = 55; Rim (inch) = 16; New tyre width = 225; New aspect ratio = 45; New rim = 17
Result: Diameter = 631.9 mm; New diameter = 634.3 mm; Difference (speedometer error) = 0.3798 %; At an indicated 100 km/h = 100.38 km/h
How it is calculated
1. Enter the values you know. 2. The calculator converts them to base units and applies the formula. 3. The result is shown in the unit you choose.
Frequently asked questions
How do I calculate it?
Given: Width (mm) = 205; Aspect ratio (%) = 55; Rim (inch) = 16; New tyre width = 225; New aspect ratio = 45; New rim = 17. Result: Diameter = 631.9 mm; New diameter = 634.3 mm; Difference (speedometer error) = 0.3798 %; At an indicated 100 km/h = 100.38 km/h.
Is the calculator free and private?
Yes. It is free, needs no sign-up and runs in your browser — the numbers you type stay on your device.