Legal

Disclaimer

Last updated: 10 November 2026. Please read this before using any tool or guide on TyreCalc.

1. Fitment safety

A wrong tyre size can cause accidents. It changes braking distance, handling, stability, speedometer accuracy, ground clearance and the load your tyres can carry. A size that is wrong for your vehicle can rub on arches or suspension, overload the tyre, invalidate your insurance or fail a roadworthiness inspection.

Before fitting any tyre size different from the one your vehicle came with, you must:

• Check the tyre size on your door-jamb placard and in your owner's manual — that is the size your car was designed and type-approved with.
• Match or exceed the original load index — never fit a tyre rated to carry less than the original.
• Match or exceed the original speed rating — never fit a tyre rated slower than the original (except a winter tyre fitted under the rules that apply in your country, and only with the required speed sticker).
• Check physical clearance — arches, suspension, steering lock and brake components — which no online calculator can verify.
• Consult a tyre professional and, if in doubt, your vehicle manufacturer or dealer.

The commonly used ±3% overall-diameter guideline is a rule of thumb used by the tyre trade to flag sizes worth investigating. It is not a safety standard, not a legal threshold, and not a guarantee that a size fits. A size inside ±3% can still be unsafe on your car; a size outside it is almost certainly a bad idea.

2. Speedometer and legal compliance

In the UK and EU, a speedometer must never read slower than your true speed, and may read fast by up to 10% plus 6.25 mph. Changing tyre size moves your speedometer error, and a larger tyre can make it read slow — which is illegal and dangerous. Our speedometer tools estimate the change; they do not certify compliance. Rules differ by country: check the rules where you drive.

3. Fuel, MPG and cost figures are estimates

Fuel cost, MPG, EV vs petrol and tyre cost-per-mile results are estimates for planning. Real fuel consumption varies with driving style, speed, load, weather, tyre pressure, road conditions and the condition of the vehicle. Pump prices and electricity tariffs change daily. Tyre wear varies with alignment, pressure, driving style and road surface. Treat every money figure as approximate.

4. Vehicle data

Factory tyre sizes listed for vehicles are given as a guide and may differ by trim, year, market or optional equipment. The only authoritative source for your car is the placard on the vehicle itself and your owner's manual.

5. No professional advice

Nothing on TyreCalc is mechanical, legal or financial advice. For advice about your specific vehicle, speak to a qualified tyre professional or mechanic. For legal questions about what you may fit, consult the regulations in your country.

6. Liability

To the fullest extent permitted by law, TyreCalc is not liable for any loss, damage or injury arising from reliance on this site, including any damage caused by fitting an unsuitable tyre, wheel or part. Fitment decisions are yours and your tyre professional's.

Questions: see the contact page.