Like most electric motorcycles, this design does not use a traditional transmission.
If a transmission is not used, the gear ratio needs to provide the right balance of acceleration, top speed, and range. Most do-it-yourself electric motorcycle conversions use a reduction ratio between 3.5 and 5.5 (number of teeth on the aft sprocket divided by number of teeth on the front sprocket).
I chose a 50-tooth rear sprocket, which is the largest one available with the Royal Enfield changeable-sprocket rear hub, an aftermarket item.
It easily fits on the hub and clears the swingarm, and gives me the ability to use a 13- or 14-tooth sprocket on the front. If I had used the stock 38-tooth rear sprocket, I would have had to use a 10- or 11-tooth front sprocket. I was afraid that a front sprocket that small might not allow the chain to clear the swingarm pivot, or might not run smoothly due to chordal action.
The front sprocket is a 13-tooth with attached collar and 7/8 inch bore. A 3/16 inch square key and two set screws are used to secure the sprocket to the motor shaft.
The chain is size 530 heavy duty (ANSI 50-H) roller chain.
It is the same gauge of chain as on the original motorcycle. The chain was bought in bulk (10 ft length), broken to fit, and connected with a master link.