Tyre Size Calculator

Compare two tyre sizes to calculate diameter differences, speedometer error, and find alternative compatible sizes. Our comprehensive tyre size calculator provides visual comparisons, speedometer accuracy charts, and intelligent alternative size suggestions including plus sizing and minus sizing options. Perfect for upgrading wheels, fitting winter tyres, or optimizing your vehicle's performance while maintaining accurate speedometer readings.

How to use:

Single Size: Enter your tyre size to view specs and find alternatives
Compare Two: Enter both sizes to see diameter differences and speedometer errors
Quick Compare: Click any alternative size to instantly compare it

Try these popular comparisons:
225/45R17 vs 235/40R18 265/70R17 vs 275/60R20 245/40R19 vs 255/35R20 205/55R16 alternatives

	Width (mm)	Profile (%)	Rim (")
Original Tyre Size
New Tyre Size (optional)

Calculator Results Charts Visual Alternatives

Measurement	Original	New	Difference	%
Width
Diameter
Circumference
Sidewall Height
Revolutions/km

Speedometer Error:

Visual Comparison

Wheel Spacing

Rotation Speed

● Original (Gunmetal) ● Comparison (Bronze)

Tip: Click Overlay to stack both tyres on top of each other and see the exact size difference. Use the camera buttons to view from different angles.

Drag to rotate • Scroll to zoom • Right-click to pan

Alternative Tire Sizes

These alternative sizes maintain a similar overall diameter (within ±2%) to your original tire.

Important Notice

All measurements, diameter calculations, speedometer error estimations, and alternative size suggestions provided by this calculator are theoretical values derived from nominal tire size specifications using standard industry formulas.

Actual tire dimensions may vary from calculated values. Tire manufacturers are permitted to produce tires within established manufacturing tolerances as defined by industry standards (ETRTO, T&RA). Actual tire dimensions can differ based on manufacturing tolerances, tread design, inflation pressure, rim width, and load conditions. Always verify fitment compatibility with your vehicle manufacturer's specifications and consult a qualified tire professional before making any tire size changes. This tool is provided for informational purposes only and should not be considered as professional advice or a guarantee of fitment or safety.

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Tyre Size Calculator

How to use:

Visual Comparison

Alternative Tire Sizes

Important Notice