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Tire Size Comparison Calculator

Two dirt-bike sizes side by side: diameter change, speedometer error, and the gearing change it feels like.

Inputs
Results
Live

  • Diameter change

    2.0mm

  • Tire A diameter

    27.3in

  • Tire B diameter

    27.38in

  • True speed if speedo assumes A

    1.003×

    You are going faster than the speedo (if it was calibrated on A)

  • Gearing feel vs A

    0.997×

    Taller — a bit more top speed, less snap

Formula

Speedo factor = new Ø / old Ø · Equivalent gearing ≈ old ratio × old Ø / new Ø

Related calculators

Tire Size
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Tire Diameter
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Tire Circumference
Rolling circumference from diameter or from a metric size. This is the number a speedometer calibration cares about.
Tire Wheel RPM
Wheel RPM and distance per revolution from speed and tire diameter — the tire-side version of the performance wheel-RPM tool.