Compare two tyre sizes and find each one’s diameter, the percentage difference and how much the speedometer deviates.
Compare two sizes
Enter the sizes as width / aspect R rim (e.g. 205/55 R16) for both tyres.
The ideal diameter difference is under ±3%, otherwise the speedometer and ABS may be affected.
205/55R16 → 225/45R17: Diameter difference +0.38%Quick calculations for drivers. Standard formulas for consumption, cost and speed. Instant in-browser calculation, no account, no data sent. Fuel prices are indicative.
The diameter is the rim plus twice the sidewall (width × aspect). The difference shows the speedometer deviation:
205/55 R16 (Ø 632 mm) vs 225/45 R17 (Ø 634 mm): +0.4%; at 100 km/h indicated, true speed ≈ 100.4 km/h.
It is the tyre size: 205 is the width in mm, 55 is the height-to-width ratio in percent, and R16 is the rim diameter in inches. From these the overall wheel diameter is computed.
Add the rim diameter (in mm) to twice the sidewall height. The sidewall is width × aspect (%). For example, 205/55 R16 has a diameter of ≈ 632 mm.
Generally under ±3% of the original size. A larger difference affects the speedometer, gearbox, ABS and may rub in the wheel arch.
Larger-diameter tyres travel farther per rotation, so the true speed is higher than shown. The calculator shows the true speed for a given indicated speed.
Often yes, within a range allowed by the rim width. Check the manufacturer’s specs and keep the overall diameter close to the original.
It is the second number in the marking and represents the sidewall height as a percent of the width. A smaller number means a lower sidewall and a sportier profile.
A different diameter changes engine rpm at a given speed and the rolling, slightly affecting consumption and the speed reading. That is why keeping the original diameter is recommended.