gear sizing

Discussion in 'Photos & Bicycle Builds' started by cox24711, Jul 16, 2015.

  1. cox24711

    cox24711 New Member

    hi everyone i have a mongoose supergoose 2008 that i am converting to a motor bike i have a stihl fs 36 cc 2stroke motor i was wondering for max speed and acceleration and hill climbing ability what gearing should i use ? i also have a centrifugal clutch built into the motor with no sprocket attached and the bike is stock

  2. LR Jerry

    LR Jerry Well-Known Member

    Depending on how much you weigh and how steep the hills are, you may need a shift kit for an engine that small.

    I'm 250 lbs. Where I live lots of 20%+ grade hills. The bike weighs 100 lbs uses 26 inch tires. The engine is a Robin Subaru 35. 4 stroke, 33 cc, 1.6 HP at 7000 rpm, 1.2 ft/lbs torque at 5000 rpm and 8000 max rpm. The 7 speed reduction range is 49.21-18.82:1.

    Max climbing torque is 59 ft/lbs. I have to lightly pedal assist on 25% grades had heavily assist on 30% grades. From an old setup I used to use a 55:1 reduction I lightly assist at 30% grades. That would give me 66 ft/lbs.

    The level ground speed is 28.8 mph at 7000 rpm. The downhill assist is 32.9 mph at 8000 rpm.

    I hope this helps some. Knowing the rpm range will really help. You can order a tach fairly cheap on eBay.
    Last edited: Jul 17, 2015
  3. cox24711

    cox24711 New Member

    hi i weigh 40 kgs and the bikes wheels are 20 inch
  4. The_Aleman

    The_Aleman Active Member

    You're not going to get "max speed and acceleration and hill climbing ability" with one gear. You can get max speed or you can get acceleration/hill climbing ability.

    With one gear, you'll always have to compromise somewhere.
  5. cox24711

    cox24711 New Member

    then what gearing should i use? for max speed
  6. The_Aleman

    The_Aleman Active Member

    I don't have near enough information to answer that question. I don't know anything about your engine or what kind of drive system you plan on using.

    Even if I knew that stuff, I wouldn't be able to recommend a gear ratio. You'll have to play around with a gear ratio calculator and do some testing to find a middle ground.