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Motorcycle vs Bicycle chain tension

  1. Nov 20, 2008 #1
    Trek recently released a belt driven bicycle (instead of chain drive) which led to a discussion among some cycling friends. Which led to discussion of torque, power output, etc. Anyway, I'm trying to compare the chain tension of a motorcycle vs the chain tension of a bicycle. I'm better with electrical systems, my mechanical systems knowledge is rusty.

    These specs are from a real motorcycle:
    engine makes 16 ft-lbf at 10,000 rpm
    primary reduction ratio is 1.9
    1st gear reduction ratio is 2.7
    Final reduction ratio is 2.7
    mass is 420 lbs

    Based on the above:
    the output shaft of the engine is 30.4 ft-lbf @ 5260 rpm
    post-transmission pushes 82 ft-lbf @ 1950 rpm
    at the rear wheel (in 1st gear) it's 221 ft-lbf, @ 720 rpm.

    Track Bicycle:
    Rider is 150lbs
    Crank arms are 170mm (0.56 ft)
    Gear gain ratio is 3:1 (normal for a track bike)
    Mass is 20 lbs

    Based on the above:
    at the crank, rider makes 84 ft-lbf
    at the rear wheel, 28 ft-lbf

    I'm not exactly sure how to calculate chain tension from here (or perhaps I've already made a mistake...) I'm thinking that I need to specify an acceleration before I can get the answer. Can't quite recall the appropriate equations.....
  2. jcsd
  3. Nov 20, 2008 #2


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    Homework Helper

    You just need the sprocket size at either end and the torque at the end that you know the sprocket size at. Then the tension = torque at the sprocket / effective radius of the sproket.
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