Tools / Tyre size calculator
Tyre size calculator: compare tyre sizes
Enter width, aspect ratio and rim size of the current and the new tyre (from the sidewall, e.g. 205/55 R16).
Current tyre
New tyre
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🔒 Runs entirely in your browser – nothing you enter is uploaded or stored.
How to use it
- Enter the current tyre size.
- Enter the new size.
- Check the difference and the speedometer effect.
Your inputs live only in the link, not on our server.
Last checked: October 2026 · Based on: ETRTO tyre designation; UNECE Regulation No. 39 (speedometers). Found a mistake? Use the form below – we fix confirmed errors and update the date.
Frequently asked questions
What does 205/55 R16 mean?
205 mm width, sidewall height 55 % of the width, radial tyre for a 16-inch rim.
How much may the diameter differ?
As a rule of thumb about −2 % to +1.5 % – but only sizes approved for your car are allowed.