Compare two tyre sizes and instantly see differences in overall diameter, sidewall height, rolling circumference, speedometer error, and ground clearance. Ideal when upgrading wheels or checking whether an alternative tyre size is suitable for your vehicle.
✔ Compare two tyre sizes • ✔ Speedometer difference • ✔ Rolling diameter • ✔ Ground clearance
Most manufacturers recommend keeping the overall tyre diameter within approximately ±2% of the original size to minimise speedometer and handling changes.
This calculator compares two tyre sizes and calculates:
A tyre marked 225/45 R17 means:
Original:
225/45 R17
Replacement:
245/40 R18
The new tyre has a very similar rolling diameter, making it a common upgrade with only a small speedometer difference.
Most manufacturers recommend staying within approximately ±2% of the original rolling diameter.
Changing tyre diameter affects:
Not necessarily. Wider tyres can increase grip, but they may also increase rolling resistance, reduce fuel economy, and be more susceptible to tramlining depending on the vehicle.
If you're modifying your vehicle, you may also find our Power Converter, Torque Converter, Power-to-Weight Calculator, Fuel Cost Calculator, Mileage Calculator, and EV vs Petrol Running Cost Calculator useful.
Calculate HP per tonne and kW per tonne to compare the performance of cars, motorcycles, and electric vehicles.
Convert instantly between Horsepower (HP), Metric Horsepower (PS), and Kilowatts (kW).
Convert torque between Newton metres (Nm), pound-feet (lb-ft), pound-inches (lb-in), and kilogram-metres (kg·m).
Compare tyre sizes, rolling diameter, sidewall height, circumference, and speedometer difference.
Compare wheel width, offset (ET), and tyre fitment to see inner and outer clearance changes.
Calculate gear ratios, final drive ratios, wheel speed, and torque multiplication for any drivetrain.
Quickly access our most popular calculators. Fast, accurate, and free — no signup required.
Browse essential calculators for finance, everyday maths, and scientific calculations — all in one place.
✔ Free • ✔ Fast • ✔ No signup required • ✔ No DATA collected
Built for personal use, now shared for free — simple, fast, and private calculators for everyone.
Last Updated: August 2026