Gear speed question

Discussion in 'Hubs, Gearboxes, Sprockets and Chains' started by Taffy13, Nov 23, 2019.

  1. Taffy13

    Taffy13 Member

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    I'm building up a bike atm, I'm wondering what top speed would be like with with 49cc engine with long exhaust 5:1 belt drive, 36 tooth rear sprocket, and 180pound rider. Not many hills around me so don't need to worry about that. I'm alsi planning to pedal start from stops. So really just wondering about top speed.
     
  2. LR Jerry

    LR Jerry Well-Known Member

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    You're leaving out some very important information. What kind of engine 2 or 4 stroke? Most 49cc 2 strokes max horse power is around 6000 rpm. Most 49cc 4 strokes max horse power is around 7000 rpm. Then you must calculate up gear reduction. Last of all wheel size must be known. The math formula would look this:

    (RPM x Wheel Diameter x ⚻) ÷ (Gear Reduction × 1056) = Speed in MPH.
     
    #2 LR Jerry, Nov 26, 2019
    Last edited: Nov 26, 2019
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  3. Taffy13

    Taffy13 Member

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    Thank you for that, now I can figure it out on my own and even adjust depending on what I want
     
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  4. LR Jerry

    LR Jerry Well-Known Member

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    On my bike which has an RS 33cc 4 stroke engine, it shifts 7 gears automatically the gear reduction ranges from 49.21:1 to 18.82:1. This gives me a level ground speed of 28 mph using 26 inch wheels.

    On the practical side 30 mph on level ground is very obtainable at your weight using a 49cc engine. Consider yourself doing very well if you can reach 35 mph.
     
    #4 LR Jerry, Nov 26, 2019
    Last edited: Nov 26, 2019
  5. Taffy13

    Taffy13 Member

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    Gotchya that makes alot of sense now with that formula, and I'm going to go with a 4 stroke 49cc. Also 26 inch wheels. 35-37 is right around where I want to be for keeping up with traffic and still being under the speed limit for motorized bikes in my area
     
  6. Taffy13

    Taffy13 Member

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    So math check
    (7000x26x pie(cant do the symbol lol)÷(18×1056) = 30 ish with a 36 tooth

    And if you change the 18 to a 14(28tooth) then itll be about 38 mph sound about right?
     

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