Motorcycle vs Bicycle chain tension

1. Nov 20, 2008

asynchronous13

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. Nov 20, 2008

rcgldr

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.