Sprockets Help with Gear ratios

Discussion in 'Transmission / Drivetrain' started by MartinNZ, Aug 17, 2013.

  1. MartinNZ

    MartinNZ New Member

    Hi all,

    I've be planning to make a chainsaw powers bicycle for a while now, but I don't know what to do for Gear ratios... The motor I am using is a 45cc chainsaw that has max rpm of 1000. i will be mounting it on a 26 inch mountain bike, using chain drive to get the power to the rear wheel. I understand that use the sprockets from the front peddles is a effective way to gear down from the motor(the bike is a 21 speed, three on the front, six on the back).

    If anyone with more knowledge than me could help that would be much appreciated.

  2. MartinNZ

    MartinNZ New Member

  3. 5-7HEAVEN

    5-7HEAVEN Active Member

    You must mean 10,000rpm, not 1,000rpm.

    Actually, the sprockets from front pedals INCREASE gear ratio.

    Why? Because the drive sprocket(pedal sprocket) is
    larger than the driven(wheel sprocket).

    You need to lower your gear ratio.
    Ironically, the higher the numerical gear ratio,
    the lower the gear ratio.

    JMO, a 20:1 gear ratio is optimum.

    To get 20:1 for a chainsaw engine is very difficult.

    You'll need a ratio of about 30:1 before you engage the drive sprocket on the pedals.

    Good Luck.
    Last edited: Sep 4, 2017