Gear ratio

Discussion in 'Transmission / Drivetrain' started by Frankfort MB's, Aug 30, 2016.

  1. Frankfort MB's

    Frankfort MB's Well-Known Member

    Im trying to figure out what my gear ratio should be on my 212cc predator..... If I'm not mistaken the sprocket coming off the motor is a 10 tooth.

    My problem is what size sprocket should I run in the rear if I want to go about 50mph at max speed?

    I appreciate any help I can get!
     

  2. CrazyDan

    CrazyDan Member

  3. MotorBicycleRacing

    MotorBicycleRacing Well-Known Member

    You can't run a chain from a 10 tooth to the back wheel on a 212 cc
    You need a jackshaft.
    The best gear ratio calculator is http://jimsitton.net/ratiocalc/
     
  4. Frankfort MB's

    Frankfort MB's Well-Known Member

    Why not?
     
  5. MotorBicycleRacing

    MotorBicycleRacing Well-Known Member

    After you play around with the gear ratio calculator you may figure it out?

    Also how wide do you think a 212 cc is?
    How are you going to line up the front sprocket with the rear sprocket?
     
  6. Frankfort MB's

    Frankfort MB's Well-Known Member

    I've looked around and I could use one rear sprocket but it would be crazy huge:)

    A 60 tooth rear and 10 front at 5000 RPMs with a 26.5in wheel (including tire)
    I would be maxing out at 66mph......

    Maybe useable??? Probably not???:D

    EDIT
    I just made sure on front sprocket size and I was off a good bit, it is actually a 16 tooth soooo.... I will have to do a jack shaft thanks for the help everyone!:)
     
    Last edited: Aug 30, 2016
  7. Frankfort MB's

    Frankfort MB's Well-Known Member

    My front sprocket is already lined up....
    That engine is wide. Very wide. I bought mine with the clutch already on it so I'm working with what I have
     
  8. MotorBicycleRacing

    MotorBicycleRacing Well-Known Member

    You use the max rpm at redline to calculate. You are cheating by using a lower rpm.

    More like 6500 rpm on an ungoverned engine.
    So more like 100 tooth sprocket for 51 mph.

    How far is your engine offset to the right to line the front sprocket up with the rear sprocket?

    There are good reasons why nobody uses only 2 sprockets and one chain line on a 212cc or even a 79 cc.
     
  9. MotorBicycleRacing

    MotorBicycleRacing Well-Known Member

    and that cheap clutch will jerk and buck trying to take off.........no fun at all.
     
  10. Frankfort MB's

    Frankfort MB's Well-Known Member

    I'm still in the early stages of building..... I still have to do some cutting

    (I've since cut this frame after this pic btw)

    Have you ever seen this clutch?
     

    Attached Files:

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