Maker & Reference
Gear Ratio MPH at RPM Calculator
MPH = (RPM × tire diameter × π) / (gear ratio × final drive × 1056). Pick the right rear-end gear for your tire size.
Speed (MPH)
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- Wheel RPM
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- Tire circ. (in)
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- KPH
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FAQ
How to pick a rear-end ratio? +
Higher (numerically larger) = quicker off the line, more highway RPM. Lower = better fuel economy, less acceleration. 3.73 is the all-around sweet spot for most V8s.
Tire size changes my MPH? +
Going from 28" to 31" tires drops indicated MPH ~10%. Speedo + odometer both read low. Recalibrate or get a tuner module.