Gear Reduction

GoldenMotor.com
Aug 26, 2015
472
6
18
Overgaard AZ
I'm running a China Girl, 66cc SD Stinger. I've got a 56t rear sprocket on the way. I was wondering if any one knows where I can find a smaller (9t) front sprocket?
I have no interest in shift-kits, as there is something to be said for simplicity.

Useing a smaller front sprocket would actually give a lower gear ratio than a larger rear, and between a 9t front and a 56t rear it should climb just about any hill with ease. Should also keep me closer to the 20mph law I'm currently blowing the doors off...

Also my recurring theme, engine longevity. If the motor isn't working so hard, it should last longer. Speed, or rather, the lack of it, is not a concern. I'm already close to twice my legal limit, and strangling the motor makes no sense to me at all.

What I'm getting at is, that I want the same power output from the motor, but about half the speed, while maintaining the simplicity of the drive train. A shift kit is not the answer due entirely to the fact that I view them as an unnecessary complication. The system works as is, I'm not going to start throwing monkey wrenches, I Just want to get up the hills and be somewhat closer to legal.

If I'm doing 40mph now how much will a 56t rear cut my top speed? I could probably get away with 25 and blame it on the motor running really good just then for some reason, or a hill or whatever, but I'd hate to get popped for criminal speed on a motorbike!laff
 

Davezilla

New Member
Mar 15, 2014
2,705
10
0
San Antonio Texas
If your top speed is 40 with the 44T rear sprocket then to bring it down to 20 mph you would theoretically need an 88T to get the top speed down that much. The 56T would bring it down to around 35ish, and if there were smaller front sprockets available you would need like a 5T up front to bring the speed down from 40 to 20.
A simple jack shaft between the engine and rear sprocket could get you the reduction you're looking for easily by running a 20T input sprocket and a 10T output sprocket, but if you don't want to go this route you may be able to find a 72T rear sprocket that should bring the top speed down to the 25 or so range for top speed, and some crazy strong hill climb ability. You could also switch down to a 24" rear wheel to help bring it down a little more...
 
Aug 26, 2015
472
6
18
Overgaard AZ
Thanks Dave, if I'm perceiving this right a "jackshaft" is essentially a GRU, or gear reduction unit? I'll look them up see what I think. Thanks again Dave, perhaps you could post a link?