Pocket Bike Motor Rear Engine Questions

Discussion in 'General Questions' started by Dr. J., Jan 28, 2007.

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  1. Dr. J.

    Dr. J. Guest

    I would like to use a pocket bike motor and place it over the rear wheel similar to a GEBE setup. It would be great to use the typical rear sprocket setup found on China motors, but the chain pitch is different. I know GEBE uses a 12-14 front sprocket, but what is the number of teeth on their rear ring (sprocket)? Maybe bamabikeguy can answer this one. The ratio could be used to find the ratio of the pocket bike motor setup since both drive off the crankshaft and have no reduction like the China motors.

    Pocket bike motors use 6-10 teeth front sprockets and can go up to about 70 teeth on the rear. A rear pocket bike sprocket could be machined to be used and mounted like the China bike setup.

    I know Haggard has done a fantastic job with gear reduction, but can sprocket combinations be used to eliminate the gear reduction?

    Dr. J.

  2. The thing is that a pocket bike has a very small wheel. When using the motor on a much larger 24" or 26" wheel, you'll very likely need a pretty large rear sprocket. You can get some pocket bike engines with a cvt gear reduction built on. If you look online you can find gear ratio calculators for mini-bikes or go-karts that may be of use to you. Do you know which chain number each bike uses?
  3. Dr. J.

    Dr. J. Guest

    China Motor #415 wide 1/2 x 3/16

    Bicycle narrow 1/2 x 1/8

    Pocket Bike #25 1/4 x 1/8
  4. Haggard

    Haggard Guest

    I can't see how and have given it plenty of thought.
    Basically to keep the same ratio as the pocket bike has but switch that ratio to a bicycle , you have to allow for the difference in wheel circumferences.
    The difference is 2.5 to 1 but I like going 2.2 to 1 . keeps my rpms a little lower at high speeds while not sacrificing any bottom end that a little pedaling wont handle.
    So basicly , if you use the 6t pinion(front sprocket). You need a 150t rear sprocket.
    Changing up the pinion will only make it worse.
    Theres no way around(in my opinion anyways) using a reduction box or a jackaxle.Learn how to make a simple, efficient jackaxle here : http://www.motoredbikes.com/showthread.php?t=7996 . also ,have a look at some of Zombies posts. He makes some incredible jackaxles.

    Good luck

  5. Haggard

    Haggard Guest

    Unfortunatly , all the reduction box does is allow you to use a much larger front sprocket.
    It doen't change a thing, you'd still need a 150t rear sprocket.
    HOWEVER, the gopeds use a reductionbox thats rated 5 to 1 I believe but reverses direction.They use the same clutch and will bolt right up.
    I have a couple of them but havent gotten around to messin with them yet. Will keep you posted.

    Last edited by a moderator: Jan 7, 2008