Motorized Bicycle Gear Calculator

Discussion in 'DIY Home Built Motorized Bicycle (non kit)' started by Dave31, Nov 27, 2008.

  1. Mightyboosh

    Mightyboosh New Member

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    Hard part is finding things when I don't now wat to look for.
     
  2. motorhedfred

    motorhedfred New Member

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    I'm trying to figure pulley sizes for a 29" tall tire with all belt drive. Near as I can tell, the tire has a rollout of 91 1/2". That would mean about 692 revolutions per mile. On a bike with the cajones to pull 60 MPH at 7000 RPM, that would be 10-1 final drive ratio, but I doubt a 99cc HF has enough.

    I have no intention of riding that fast, or revving that hard....it just seemed like numbers easy to work with in my head with my own wierd formula.

    I'm not sure what to shoot for.
     
  3. Mightyboosh

    Mightyboosh New Member

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    Yeah I don't know of a calculator for for a belt drive. Even then it wont be right. It tells the speed of the tire with 0 weight and 0 resistance. My predator gets to above 45 but the calculator said it do 90. Make sure u take out the complete governor mechanism. Other wise u wont get close to 7000rpm.
     
  4. motorhedfred

    motorhedfred New Member

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    I should mention that I was calculating around a 3" drive roller FD.
     
  5. ducatiluke

    ducatiluke New Member

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    my 148cc runs 6:1
    my 31cc runs 22:1
    so 10 to 1 for a 99cc sounds like a good starting point
    10:1 at 7000 rpm with 29" should give you 17mph at 2000rpm
    and 60mph at 7000 rpm

    love to post pictures but this web site has size limits

    i have a great program that gives you speeds after u enter all data ratios
    wheel size rpm ect
     
  6. MotorBicycleRacing

    MotorBicycleRacing Active Member

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    Best gear ratio calculator!

    The program can be downloaded from http://jimsitton.net/ratiocalc/

    Just right click on the file gearratio.exe

    and select "save link as" and put it somewhere you can find it again.

    Once it's saved, double click on the gearratio.exe file and it will run.

    The program allows for up to three ratios in series.

    If you have fewer just leave the unused ratios set to 1:1.

    The program will also calculate speed based on
    engine RPM,
    drive ratio,and
    wheel diameter.


    Be sure to measure the outside diameter of your wheel for accurate results.
     

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