Force will be the same, but the torque will be higher.

Torque = force X distance

http://en.wikipedia.org/wiki/Torque

The load on the chain depends on what cog sizes you are using.
For the same gear ratio, 2:1 equivalent (same gear inch), a larger front cog will give a lesser load on the chain.

For a scenario of a rider and bike weight of 89.5kg riding up a 10:1 slope the torque on the hub (~30Nm) remains the same regardless of wheel size or cog size for the same gear ratio (2:1). So to does the torque created by the front chainring (~56Nm). A longer crank will require less pressure on it than a short one.

The one thing that does change dramatically is the tension on the chain.
The bigger the chainring the less load on the chain:

29" wheel, 40/22 = 70.3 kg
29" wheel, 36/20 = 78.1 kg
29" wheel, 32/18 = 87.9 kg
26" wheel, 40/20 = 70.3 kg
26" wheel, 36/18 = 78.1 kg
26" wheel, 32/16 = 87.9 kg

So by adding 8 teeth onto your chain ring you will reduce the load on the chain by up to 20%.
Imagine the loads you are creating when you are cranking up a steep section in your granny gear and try to force a gear change.

Technically given all other variables are the same apart from the crank arm lengths force would be less with torque staying the same. Which means no change to force the chain is under.

Any how the breaking strain on a bike chain will be far higher then most people could produce. The chain is twisting for some reason which is very very bad when you load it up. Mostly due to the design of the chain.
Torque is a rotational unit of measure and not applicable to a chain. So means fuck all if you have wheels 20" or 29"


Don't use wiki its not always correct.
Could email Dougal and ask if any one has a spare day or two to read the reply.

Exactly. The breaking strain of a ss chain is in the vicinity of 1300kg.
Even stomping on a gear ratio for a granny gear of 22/28 produces about 390kg of tension.

Garth wrote:The load on the chain depends on what cog sizes you are using.
For the same gear ratio, 2:1 equivalent (same gear inch), a larger front cog will give a lesser load on the chain.

For a scenario of a rider and bike weight of 89.5kg riding up a 10:1 slope the torque on the hub (~30Nm) remains the same regardless of wheel size or cog size for the same gear ratio (2:1). So to does the torque created by the front chainring (~56Nm). A longer crank will require less pressure on it than a short one.

The one thing that does change dramatically is the tension on the chain.
The bigger the chainring the less load on the chain:

29" wheel, 40/22 = 70.3 kg
29" wheel, 36/20 = 78.1 kg
29" wheel, 32/18 = 87.9 kg
26" wheel, 40/20 = 70.3 kg
26" wheel, 36/18 = 78.1 kg
26" wheel, 32/16 = 87.9 kg

So by adding 8 teeth onto your chain ring you will reduce the load on the chain by up to 20%.
Imagine the loads you are creating when you are cranking up a steep section in your granny gear and try to force a gear change.

Thanks for the maths, good to see that I was right about the load on the chain also why companies like Shimano make tougher freehubs for 29ers.

To re-leave suckers of their money?

beer & pies .......... mmmmmmmmmmmm pies

Always a delight to spark debate.

Picking the bones out of that lot perhaps it's a combination of twisting + increased torque. Twisting would probably be sticking in the granny ring rather than changing up and hence cross-chain running.

Last breakage was Sunday and I'd lost the use of my thumbs by Leaping Lizard so getting into the middle ring was an issue...

I do have a 36-12 and I've only snapped one chain on that cassette. Oh, and spun the freewheel ratchet insert in a rear hub - but there can't be more torque though, can there

Anyway, I've got the answer to my original post - it's not a common problem.

Simpleone wrote:Thanks for the maths, good to see that I was right about the load on the chain also why companies like Shimano make tougher freehubs for 29ers.

So by your reckoning a chain is under more tension in on a 29er than a 26er for any given gear assuming the same force is exerted on the crank?

keep it in the classroom...

pducky wrote:keep it in the classroom...

Is this Vorb, or MTBR.com?