Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

How do i figure how much torque i need?

  1. Sep 2, 2008 #1
    I am building an "alternative fuel" motorcycle.

    But i am having trouble figuring out what size motor i need to use and how much torque it needs to put out.

    I have already figured out my top speed, (I am limiting the prototype) and also the RPMs of the drive tire at that speed. I also have the estimated weight of the completed bike with rider.

    I am looking for a formula to determine how much torque is needed.

    Thanks for the help.
  2. jcsd
  3. Sep 2, 2008 #2


    User Avatar

    Staff: Mentor

    Torque determines the acceleration. Top speed is a difficult thing to calculate due to it being largely dependent on wind resistance. Regardless, why not just look at the specs of similar motorcylce motors?
  4. Sep 2, 2008 #3
    Russ 's advice is good - look at existing designs. Also, the gearing you select will make a big difference too. Motorcycle transmissions in top gear are 1:1, so you need to consider the primary gearing (engine sprocket to gearbox input sprocket) and the final gearing (gearbox output sprocket to wheel sprocket). These ratios translate the engine torque to the rearwheel torque.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?