79cc gear ratio?

Discussion in 'DIY Home Built Motorized Bicycle (non kit)' started by waynesdata, Jul 23, 2017.

  1. waynesdata

    waynesdata Member

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    Most kits I have seen have the same default gear setup.

    Motor Sprocket 11 tooth
    Jackshaft Input Sprocket 22 tooth
    Jackshaft Output Sprocket 9 tooth
    Wheel Sprocket 44 tooth
    Tire Height 26“

    Is this gear ratio ok?
     

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  2. TheNecromancer13

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    That gear ratio is about 9.78:1, way too steep for a 79cc predator. You'll burn up your clutch and won't be able to go up hills. I have mine geared at 13.1:1, I weigh 155 lbs, it tops out at 40 mph. I wouldn't recommend buying the kit though, most of the parts are **** and it doesn't include everything you'll need to build the bike. Here's what I do: https://www.instructables.com/id/79cc-Motorized-Bicycle-From-Scratch/
     
    Dan and MotorBicycleRacing like this.
  3. Dan

    Dan Staff
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    Wayne, I misread and messed up the math. Necro is 100% correct. But do love that jackshaft. I can't make one from scratch for that price ($99 as of this post) Really is stout and well finished. I deleted my bad advice so as not to cause confusion.

    I just use a larger rear sprocket. 54T gives you 12:1.

    9:1 would work but is not fun at take offs. Shudders real bad. I did not burn threw any clutches but am sure I would have eventually and I was using less then 9.78:1 .

    What did you decide on doing?
     
  4. waynesdata

    waynesdata Member

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    I do not know yet. I got a frame from gasbike when I ordered wheels. Will need to find out if the four stroke mounting hardware will clear my built in mount.
     

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