How to use this calculator
- Enter the requested journey or vehicle details.
- Select the matching units and options.
- Choose Calculate to see the estimate and supporting values.
- Change any value and calculate again to compare scenarios.
How the calculation works
Sidewall is width multiplied by aspect ratio. Overall diameter adds two sidewalls to wheel diameter.
Formula: Diameter mm = wheel inches × 25.4 + 2 × width mm × aspect ratio ÷ 100.
Worked example
A 205/55 R16 tyre has an approximate diameter of 631.9 mm.
What can affect the result?
Clearance, load and speed ratings, wheel width, offset and manufacturer approval must also be checked.
Tyre compatibility notice
This calculator provides mathematical comparisons only. Verify load rating, speed rating, clearance, wheel compatibility and approved sizes with the vehicle manufacturer or a qualified tyre professional.
Frequently asked questions
What difference is acceptable?
The tool does not approve compatibility; ask the vehicle manufacturer or a qualified tyre professional.
Is speedometer change exact?
No. It is an approximate mathematical comparison.
