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question for the mechanical minded peeps
02GF74 - 19/8/11 at 07:51 AM

Question is about the the force in a chain on a bike - which one would have bigger force going through it:

1. driving gear 39 T, driven gear 23 T (e.g. road bike)
or
2. driving gear 22 T, driven gear 32 T (e.g. mountain bike)

The motor unit (i.e. the cyclist) is generating the same amount of torque.

I also assume the greatest force is in the lowest gear - is that correct?

cloudy - 19/8/11 at 07:59 AM

The force "seen" by the chain is only affected by the torque going into thecrank by the rider and the size of the sprocket driving it. The rear sprocket makes no difference to this force. Therefore the 22T mountain bikes chain would be under greater stress...

[Edited on 19/8/11 by cloudy]

sebastiaan - 19/8/11 at 08:14 AM

correctamundo! ;-)

sprouts-car - 19/8/11 at 08:18 AM

quote:
Originally posted by cloudy
The force "seen" by the chain is only affected by the torque going into thecrank by the rider and the size of the sprocket driving it. The rear sprocket makes no difference to this force. Therefore the 22T mountain bikes chain would be under greater stress...

[Edited on 19/8/11 by cloudy]



Surely the attainable force also depends on the load and therefore the rear sprocket?

Ie with nothing on the back end, the maximum force will be very low if not 0.

I understand that in the static case (holding the back wheel fixed) then the size of the rear sprocket is irrelevant.

kipper - 19/8/11 at 08:38 AM

I have been a cyclist all my life and have often wondered how much horse power a man can make!
sorry to highjack this post .
anyone know?
Denis.

sprouts-car - 19/8/11 at 08:52 AM

quote:

The power a human can generate is highly dependent on the duration of the effort. In a four-second burst, a weightlifter might generate 3 horsepower. A world-class cyclist will generate 0.65 hp for a 1-hour time trial -- all-out effort. Most recreational cyclists generate about 0.35 hp for a sustained (2 hour) ride.

Macbeast - 19/8/11 at 09:27 AM

But he said the rider is generating the same amopunt of torque so it's irrelevant whether the back wheel is stationary or going up a hill.
The tension depends on the diameter ofthe driving sprocket

[Edited on 19/8/11 by Macbeast]

02GF74 - 19/8/11 at 09:37 AM

quote:
Originally posted by cloudy
The force "seen" by the chain is only affected by the torque going into thecrank by the rider and the size of the sprocket driving it. The rear sprocket makes no difference to this force.


yes, I agree now.