Convert revolutions per minute [rpm] to kilometers per hour [km/h] with gear ratio and vice-versa

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General diagram of the conversion from revolutions per minute to kilometers per hour with a reduction ratio

Convert any value from / to revolutions per minute [rpm] to kilometers per hour [km/h], angular velocity to linear velocity with gear ratio. Fill one of the following fields, values will be converted and updated automatically.

revolutions per minute [rpm]
rpm
gear ratio (1:x)
ratio (1:x)
radius [m]
radius [m]
kilometers per hour [km/h]
km/h

Formulas

Explanation

First let's consider the gear ratio. The ratio divides the input angular velocity according to the following formula:

$$ N^{output}_{(rpm)}= \dfrac { N^{input}_{(rpm)}}{ratio} $$

The angular velocity of the wheel (in rpm) can be converted into \( m.s^{-1} \) thanks to the following formula:

$$ v_{(m.s^{-1})} = r \times \omega_{(rad.s^{-1})} = r \times \frac {2 \pi }{60.ratio}.N^{input}_{(rpm)} $$

It becomes easy to convert this linear velocity expressed in \(m.s^{-1} \) into \(km.h^{-1} \) thanks to the following formula:

$$ v_{ (km.h^{-1}) } = \frac {3600}{1000}.v_{(m.s^{-1})} = \dfrac{3.6}{ratio} \times v_{(m.s^{-1})}$$

By merging the two previous equations, we can deduce the relationship between revolution per minute [rpm] and kilometers per hour [km/h]:

$$ v_{ (km.h^{-1}) } = \frac {3600}{1000} \times r \times \frac {2 \pi }{60.ratio}.N_{(rpm)} = \frac {3}{25.ratio}. \pi. r . N^{input}_{(rpm)} $$

et vice versa:

$$ N^{input}_{(rpm)} = \frac {25.ratio} { 3. \pi . r} v_{(km.h^{-1})} $$

See also


Last update : 11/03/2022