A little math?

Question

i found a bike chain and it can withstand 1300Kgf.

so i bought it thinking i can ride my haro more hardcore

so one day i pedaled like h**l to hit a quarterpipe SNAP!

and i have the right gearing and all that 13/36 and i was just wondering how much power or torq i put on it whin i was pediling?

Answer 1

A Kilogram -Force or a Kilopond (no I'm not making that up) is the force exerted by a 1kg weight subjected to gravity. This will also equal 9.81 Newtons of force.

If the chain was rated to 1300 Kgf then you should have been able to hang 1300 kg off it. It is most likely that your chain was either worn or damaged.

To generate 1300 Kiloponds of force at the rear sprocket would require the equivalent of over 200 kgs of weight to be applied to 170mm cranks (in the 9-3 O'clock position) (cranks and gearing acts as a force multiplier)

Just for the exercise we will assume the chain was ok. Here is how you would work out the torque and power.

If you have a 36 tooth chainwheel the circumference will be 18 inches (1/2 inch links). Convert the inches to metric divide by pi divide by two. You should wind up with a radius of 72.77  mm. Your 1300 kgf will need to be multiplied by gravity (9.81) to bring it to units of newtons.(12753 newtons).

Torque would then be (***edit sorry late nights times not divide)12753*.07277 newton metres.(928 NM). Note: the force at the pedals will be less but the distance will be greater, therefore the torque will be the same. The force will be greatest at the rear sprocket where the distance (radius) is smallest

For power you need to know the pedalling speed (cadence) Then power in Watts = 1300kgf x gravity (9.81m/ss) x circumference of chainwheel (18 inches converted to metres) / cadence (revs/second)

Still curious?