86
Speed = 12 = 12 = 2,083 feet per minute
GEAR RATIO
Gear ratio is defined as the number of revolutions a driving gear makes to turn a driven gear through one
complete revolution. By convention, a 4 to 1 gear ratio is said to be lower than a 2.5 to 1 ratio. Note that it
is possible to have a gear ratio of less than unity. For a pair of gears, the ratio is found by dividing the
number of teeth on the driven gear by the number of teeth on the driving gear.
Example 1
There are 27 teeth on the primary drive gear on a certain motorcycle, and 60 teeth on the primary driven
gear. What is its primary reduction ratio?
Teeth on driven gear 60
Gear ratio = Teeth on driving gear = 27 = 2.22 to 1 (rounded off)
Example 2
In a certain transmission, there are 27 teeth on 5th input (driving) gear, and 26 teeth on 5th output
(driven) gear. What is the gear ratio?
The same formula works equally well for engine and rear wheel sprockets.
Teeth on driving gear 27
Gear ratio = Teeth on driven gear = 26 = 0.96 to 1 (rounded off)
Example 3
There are 15 teeth on the engine sprocket on a certain bike, and 49 teeth on the rear wheel sprocket. What
is the final reduction ratio?
Reduction ratio = Number of teeth on driven sprocket = 49 = 3.27 to 1
(rounded off)
Number of teeth on drive sprocket 15
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