Tyre size calculator

Put your current size on one side and the size you are thinking of on the other. Every difference is shown as a plain number with its unit.

Current tyre

Width Profile Rim

New tyre

Width Profile Rim

Speedometer reading, km/h

Measurement	Current tyre	New tyre	Difference
Sidewall height	—	—	—
Radius	—	—	—
Overall diameter	—	—	—
Circumference	—	—	—
Revolutions per km	—	—	—
Revolutions per mile	—	—	—
Speed	—	—	—

Worked from the three sidewall numbers alone. Real tyres of the same size vary by a few millimetres between makers; ring us before changing size.