Gear Ratio, 4:1 final drive?

I have a 12 tooth centrifugal clutch -> 12 tooth jackshaft sprocket
Then the second jackshaft sprocket is 10 -> 40 wheel sprocket (both original to the bike)

Thats a final drive ratio of 4:1
Now im not sure exactly why I bought the 12 tooth jackshaft sprocket (bought it 3 years ago, bike has just sat since then with engine issues) but would this be a reasonable gear ratio?

I havent driven it yet, its now a 6.5 clone and my throttle, brakes, wheel bearings, new jackshaft etc etc are ordered.

Since im totally redoing the wheels, and my jackshaft assembly I thought I would ask.
Should I replace the 12 tooth jackshaft sprocket with something larger?

Will I burn out the clutch?


Active Member
the average mini is about 6 to 1. but the 4 to1 will work with the larger clone engine on flat ground for high speed. If you want to use the bike for trail riding you will want to gear it down some. That is no problem with a jackshaft, just swap out the clutch side gear for a larger one. With both gears the same size you are getting no benefit from the jackshaft . Right now it's the same as if the clutch were hooked directly to the rear wheel you are getting no gear reduction from it.
I took out my mini bike the other day with a modded clone around 12hp and with a 4:1 ratio is not what you want. In grass it was difficult to go anywhere and had no torque at all. I swapped my jackshaft gears around and the gear ratio was about 7.6:1 and with that horsepower it's a bit scary. I would suggest a 6:1 for sure. Seems like a good medium.


Well-Known Member
I've played around a bit on a couple different bikes, and found the closer to 6 to 1 i stay the better it is.

I had my super bronc geared up, it would still take off fine, but it was scary fast :scooter: