Speedometer Error Calculator
A free, browser-based calculator. Runs entirely in your browser — no sign up, nothing stored.
100% FreeRuns in your browserBasic
Enter Values
Enter your values and press Calculate to see results.
How to use this calculator
- Enter your original and new tyre diameters and an indicated speed.
- Read your actual speed and the % error.
How it works
Actual speed = indicated × new diameter ÷ original diameter. Bigger tyres mean you're going faster than the speedo shows.
Worked example
632 → 650 mm at 100. Actual ≈ 103 (about +2.8%).
Tips
- Runs entirely in your browser. Your inputs are not saved or transmitted.
Frequently asked questions
Will bigger tyres fail inspection?
Many regions limit how much you can change overall diameter — check local rules.
Privacy?
Runs entirely in your browser. Your inputs are not saved or transmitted.
Related tools
Tip: Enter any known values to calculate the remaining results.
All calculations run in your browser. Your inputs are never saved or transmitted.