Tyre size calculator;
Thinking about a plus- or minus-size fitment? Check how it changes diameter, circumference and your speedometer before you buy.
Compare two tyre sizes
See how a different size changes overall diameter, rolling circumference and your speedometer reading.
Within the ±3% safe range - speedometer and geometry stay accurate.
Client-side estimate from nominal dimensions; real tyre diameters vary slightly by model.
How the calculation works
Overall diameter is the rim diameter plus twice the sidewall height (tyre width × aspect ratio). Rolling circumference is diameter × π. A different diameter changes how far the wheel travels per turn, which is what shifts the speedometer.
- Keep the new diameter within ±3% of the original to stay speedo-accurate and geometry-safe.
- Plus-sizing (wider tyre, lower profile, bigger rim) usually keeps diameter while sharpening handling.
- Always confirm the load and speed index still meet your vehicle's requirement.
FAQ
How much size difference is safe?
Keep overall diameter within ±3% of the factory size. Beyond that the speedometer reads wrong and suspension/ESP calibration can be affected.
Does a bigger rim mean a bigger tyre?
Not necessarily - a bigger rim with a lower profile can keep the same overall diameter. That is the point of plus-sizing.
Find tyres in your size
Once you know a safe size, see what's in stock.
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