Wheel RPM from Speed
Calculates wheel rotation in RPM from tire diameter and vehicle speed in km/h.
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Wheel rolling: RPM and speed
Every revolution, a rolling wheel covers one circumference (π × D), which gives v (km/h) = π × D (m) × RPM × 60/1000. Take a 16" rim with a 205/55 tire: its overall diameter D works out to about 631 mm. At 60 km/h that wheel spins near 504 RPM, and at 100 km/h it climbs to roughly 841 RPM. Fit a taller tire, say a 205/60, and the same RPM now carries you faster than before, so the speedometer ends up reading low.
Applications
Keeping a speedometer honest after a tire or rim swap. Matching bicycle cadence to speed. Sizing an industrial motor or conveyor. Calibrating an electric scooter. Checking how many ABS sensor pulses you get per revolution.
FAQ
Why does my speedometer read wrong after a tire change? The ECU still assumes the original D. A larger tire covers more ground per revolution, so your real speed runs higher than what's shown, and a smaller tire flips that the other way.
How do I compute the tire diameter from the sidewall code? Read it off the markings. For 205/55 R16: D = 16 × 25.4 + 2 × 205 × 0.55 mm ≈ 632 mm.
Does tire wear affect this calculation? It does, a little. A worn tire can lose 5-10 mm of diameter, which nudges the RPM up slightly at any given speed.
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The results provided by this tool are for general informational and educational purposes only and do not constitute professional, financial, medical, legal, tax or accounting advice. Always confirm important decisions with a qualified professional and official sources.