| This page compares the
gearing obtained with the three-speed Sturmay Archer AW (wide range) hub
gears, with that obtained from another bicycle - a Raleigh 10-speed racing-style
bicycle (Simplex derailleur gears).
The graph shows the distance travelled for one revolution of the pedal-crank.
(I am not sure if this is the recognised way to express the effect of gearing,
but it is what I have used for the moment).
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The SA gears in conventional form cover a good range when compared to the
Simplex system - only falling short on low gears (making hill climbing
harder withthe hub-gears).
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If the SA hib gear is fitted with a Cyclo twin-sprocket and Benelux derailleur,
then two three-speed range are obtained (brown line). Perhpas a better
combination would be to fit a Cyclo sprocket with 17 and 20 teeth.
Parameters used to calculate the gearing chart were:
-
Hallmark: chain wheel = 48t, hub sprocket = 19t, wheel diameter = 28 inches,
SA-AW ratios of 4:3, 1:1, and 3:4 (for gears 1, 2, 3 respectivelt).
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Raleigh/Simplex: chain wheel = 42 & 52 teeth, hub sprocket = 28, 23,
20, 17, 14 teeth, wheel diameter = 27 inches.
(Note that the effect of pedal-crank length is not catered for in this
analysis. In all cases below, the crank is 6.5 inches long. A shorter crank
would require greater force to propel the bicycle, even though the gearing
ratio is held constant.) |
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