Jackshaft Hopeless gearing?

Discussion in 'Transmission / Drivetrain' started by Charles Laypool, Feb 5, 2016.

  1. Charles Laypool

    Charles Laypool Active Member

    Im just trying to figure out what gearing is best for me with a jackshaft kit

    If my motors Max rpm is 5500 and its internal gear reduction is 4.1 so my output sprockets rpm is 1341.4634146
    So 10t to 17t is 1.7:1
    (789.09612623 rpm)
    17t to 10t is 1.7
    (469.17419194 rpm)
    10t to 44t is 4.4444444444
    (105.49413453 rpm(at the pedals)
    44t to 36t is 1.2222222222 (86.313382798 rpm(to rear tire)
    Now if i calculate

    Axle teeth / Pedal teeth = gear ratio.

    Sprocket RPM / Gear Ratio = Wheel RPM (wRPM)

    Tire circumfrence in feet * wRPM = feet per minute.

    Feet per minute * 60 = feet per hour.

    Feet per hour / 5280 = miles per hour.


    Now i really hope im doing something wrong i ordered my shift kit im jus waiting to get it but i want to get best gearing and these results are crap someone enlighten me

  2. bakaneko

    bakaneko Active Member

    What is going on here? You are going from 10T to 17T at 1:1.7 for 1341 to 789 RPM. And, then you are going from 17T back to 10T for 789 to 469 RPM. Wouldn't it be back to 1341 RPM? Also, there is a 10% power reduction when using a jackshaft apparently. Cheers
  3. Charles Laypool

    Charles Laypool Active Member

    Ooooo snap see i knew i was missing something. Thank u for the info
  4. bakaneko

    bakaneko Active Member

    No problem, m8. We all make mistakes. I suspect the new speed numbers would be much higher now. Have fun and stay safe! :cool: