Tyre size calculator

Enter your current and new tyre size exactly as printed on the sidewall. Motorcycle sizes (120/70-17, 3.00-21) and ATV/quad inch sizes (25x8-12) both work.

Result

	120/70-17	120/60-17
Width	mm	mm
Sidewall height	mm	mm
Diameter	mm	mm
Circumference	mm	mm
Diameter difference	%
When the speedometer shows 100 km/h, your actual speed is	km/h

Results are calculated estimates. Always check your vehicle manufacturer's instructions.

Matching products: Tires ATV, UTV, Quad tires

How to use

Read the size on the tyre sidewall and type it as shown (e.g. 120/70 ZR17 or 25x8.00-12).
Motorcycle size 120/70-17: width 120 mm, sidewall height 70% of the width, rim 17 inches.
ATV size 25x8-12: overall tyre diameter 25 inches, width 8 inches, rim 12 inches.
Compare the result: a diameter change of more than ±3% noticeably affects the speedometer and handling.

Frequently asked questions

Can I fit a different tyre size?

A small difference (under 3%) is usually acceptable, but check the vehicle registration document and the manufacturer's instructions.

Why is my speedometer wrong?

A tyre with a larger diameter covers more distance per revolution, so you are actually going faster than the speedometer shows.

How do I read an ATV tyre size?

ATV and quad tyres usually have an inch size like 25x8-12: the first number is the overall tyre diameter, the second the width and the last the rim diameter, all in inches. Some ATV tyres use a metric size such as 205/80-12 – the calculator understands both.

Can ATV front and rear tyres be different sizes?

Yes, that is normal – e.g. 25x8-12 at the front and 25x10-12 at the rear. On a 4x4 ATV the ratio between front and rear diameter must stay within the manufacturer's limits, otherwise the drivetrain is stressed.

← All calculators