Need help getting a good gear ratio

[creper210210]

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]

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]

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.

I was thinking for the front 12 or 13 tooth, would that work?

 

[Venice Motor Bikes]

I was thinking for the front 12 or 13 tooth, would that work?

Try a 12t & see how it feels.

 

[creper210210]

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]

Look at what sprocket size and wheel diameter came with the motorcycle that the engine came off of.