Tyre Size Calculator
Compare two tyre sizes: overall diameter, sidewall height, circumference and the effect on the speedometer.
Tool
How to use it
Enter your current size and the size you are considering, for example 205/55 R16 and 225/45 R17. The table updates as you type.
How it is calculated
Sidewall = width × aspect ratio ÷ 100. Overall diameter = rim diameter × 25.4 + 2 × sidewall. Circumference = π × diameter. Revolutions per km = 1,000,000 ÷ circumference (mm). The speedometer reading changes in proportion to the diameter. A difference above about 3 % is usually not recommended; check approved sizes in your vehicle documents.