Need help getting a good gear ratio

creper210210

New Member
Sep 14, 2021
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I'm currently building a 125cc 4 speed manual motor onto a bicycle but I'm unsure what sprocket sizes I should chose. I want to have a decent amount of top speed (80kmh should be easy with a 4 speed transmission) but still have acceleration around the city. Any help is appreciated.
 

Venice Motor Bikes

Custom Builder / Dealer/Los Angeles
Mar 20, 2008
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Los Angeles, CA.
It's really hard to give a exact sprocket size without knowing the details of your engines internal gears... but I suggest starting with a 44t rear sprocket & test riding it.
 

creper210210

New Member
Sep 14, 2021
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The other thing that I was worried was that the rear sprocket would be so small that I am unable to use all the rpms of the engine.
 

Larry Trotter

Active Member
Nov 26, 2017
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Look at what sprocket size and wheel diameter came with the motorcycle that the engine came off of.