Speedometer change from tire size: calculation and limits
Speedometer change from tire size: calculation and limits
The calculator estimates the change caused by nominal tire geometry, relative to the original size. It cannot determine the speedometer’s total error or a legal pass/fail result without the original calibration and applicable test.
Speedo @ 100
A larger diameter increases distance per revolution. If the original indication were exact and calibration unchanged, 100 km/h indicated would correspond to 100 × new diameter ÷ original diameter. Factory bias, measured rolling circumference, wear, pressure and slip can change the real result.
ΔD (%) = (D₂ / D₁ − 1) × 100
Worked examples: original 205/55R16
| New tire | ΔD (%) | 100 km/h → |
|---|---|---|
| 215/55R16 | 1.74 | 101.74 km/h |
| 215/60R16 | 5.14 | 105.14 km/h |
| 225/45R17 | 0.38 | 100.38 km/h |
| 225/55R17 | 7.50 | 107.50 km/h |
| 195/55R16 | -1.74 | 98.26 km/h |
Editorial preset
These are TireFitLab editorial diameter-screening presets. Regional names choose a preset, not a national legal limit, ETRTO rule or vehicle approval. The AWD preset does not establish an allowable drivetrain mismatch. Use the exact vehicle and tyre manufacturer instructions; nominal geometry alone cannot approve fitment.
Detailed reference pages
Choose a common value or size to open its calculated data and explanation.
Seasonal check
Winter tire rules coming up?
Check tread depth, markings and local winter requirements before the first cold spell instead of waiting for the appointment rush.