Gear Ratios
2025-06-20
Calculation of Shifting Cadence for Sturmey Archer A2H
The calculation is solely based on official Sturmey Archer information that the hub shifts at 11.1 km/hr in a 16 inch wheel. This is approximate, as it refers to the actual size of wheel (16”), and does not consider the height of the tires or variations in tires.
The radius of the wheel is 8” or 8x2.54, or 20cm, or 0.2m
A linear speed of 11.1 km/hr is equivalent to 11,100m/hr, or 185m/min, or 3.08m/sec
The rotational speed or the angular velocity is 3.08m/sec ÷ 0.2m, or 15.4 radian/sec.
1 radian per sec is 9.55 RPM, so 15.4 radian/sec is equivalent to 147 RPM, which is the how fast the hub is turning, when it will shift.
Considering sprocket/chainring ratio
If sprocket is 15T, and chainring is 44T, the gear ratio is 2.933,
147 ÷ 2.933, is 50.1 RPM, or 50 cadence. This is the approximate cadence at which the hub will shift.
The radius of the wheel is 8” or 8x2.54, or 20cm, or 0.2m
A linear speed of 11.1 km/hr is equivalent to 11,100m/hr, or 185m/min, or 3.08m/sec
The rotational speed or the angular velocity is 3.08m/sec ÷ 0.2m, or 15.4 radian/sec.
1 radian per sec is 9.55 RPM, so 15.4 radian/sec is equivalent to 147 RPM, which is the how fast the hub is turning, when it will shift.
Considering sprocket/chainring ratio
If sprocket is 15T, and chainring is 44T, the gear ratio is 2.933,
147 ÷ 2.933, is 50.1 RPM, or 50 cadence. This is the approximate cadence at which the hub will shift.
