Tyre Size Comparison Calculator
Compare any two tyre sizes: overall diameter, sidewall, circumference and the speedometer error a swap would cause. The ±3% diameter rule is applied automatically.
Compare two sizes
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How to read the result
Staying within about ±3% of the original overall diameter keeps the speedometer, odometer and gearing close to standard — beyond that, clearance, ABS calibration and insurance become real questions. A larger diameter makes your speedo under-read (you travel faster than indicated); smaller over-reads. Diameter is only half the check: the new size must also suit your rim width, clear the arches and meet the placard's load index and speed rating.
Each size in the tool links to its own reference page — or browse all sizes. To confirm what your car should run, look up your car's full specs, including OE tyre sizes, at 247VehicleCheck.
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Last updated:
Data: computed reference values (ETRTO tyre-size arithmetic), build date 22 July 2026. Reference only — always follow your vehicle manufacturer's placard or handbook.