Force in a chain?

[02gf74]

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?

 

[Unclejack]

wouldn't the force on the CHAIN in both instances be the same, just that the force exerted on the WHEEL would be different?

 

[02gf74]

nope ... I've thought about it and posted on another forum and the rear gear is irrelevant.

the biggest tension will be with the smallest chainwheel.

 

[Unclejack]

My interpretation of your question (or what I’ve been pondering) was about the force on the chain, or is more force exerted on it (is it more likely to break) when in a low gear.
My answer to this is still “NO” it’s the same, based on the following. If we view it as three connected levers, two vertical (A and C) and one horizontal representing the chain connecting them, then irrespective of where the horizontal lever B is mounted to lever A, surely B can only move with the force applied from A and we have said that this is a constant.. But if someone dressed in brown with a beard and elbow patches would like to provide a proper answer in a good old Open University fashion then that would be appreciated . See, this question is retro...

 

[We_are_Stevo]

There are too many variables at play here, and not enough information provided, to give a definitive straight answer;

However, the one constant is that the greatest amount of torque applied/transmitted through the chain would be from a standing start on a steep incline, with the greatest force being applied on the initial downstroke on the drive side - in which case the road bike is using the greater force because it is using a higher gear to create a mechanical advantage (commence forward motion...).

This greater force is proportionally greater still in the length of chain between the top of the sprocket at the back and the top of the chainring at the front, it then decreases slightly until the same point of the next pedalling stroke is reached. The tension through the derailleur is minimal (unless you try and change gear during the pedalling stroke, but THAT is a whole different ball game!) as it is there to do two things only, take up the slack opposite the tight side (top) of the chain and move the chain from side to side across the block/cassette.

If you were to imply that your comparison point is two cyclists, one on each type of bike, cycling together on eaxctly the same stretch of flat road in ideal conditions in the same relevant gear then the road bike is still exerting the greater force on the chain (on the downside of the pedalling stroke on the drive side...) due to the mechanical effect of the higher ratio gears (unless of course the mathematics shows that the proportional forces at work are INDEED the same!).

http://www.scribd.com/doc/62497413/Powe ... -and-Chain

You do the math's - I've been up since 3AM and have a splitting headache already thankyou - and my brown coat is in the wash...

 

[02gf74]

^^^^ even so, with the maximum torque applied by the cyclist, whether moving or stationary, the maxiumum force in the chain would be when it is on the smallest chainwheel.

the crank and chainwheel are two levers, making the chainweel smaller (i.e the second lever shorter) will increase the amount of force that can be exerted by it.

(from a real world experience point of view, mnost chain mishaps occur when hoiking yup hills in the granny front gear).

 

[Pierre]

I read "chainwheel" as "chainring", i.e. the cog attached to the cranks. I'd suggest using "sprocket" as the word for the cog attached to the rear wheel, it makes the terminology less confusing!

: P

 

[We_are_Stevo]

^^^^ even so, with the maximum torque applied by the cyclist, whether moving or stationary, the maxiumum force in the chain would be when it is on the smallest chainwheel.

the crank and chainwheel are two levers, making the chainweel smaller (i.e the second lever shorter) will increase the amount of force that can be exerted by it.

(from a real world experience point of view, mnost chain mishaps occur when hoiking yup hills in the granny front gear).

Surely that wasn't your original question - you were comparing Road to MTB; which exerts the most?

Using your argument you may as well say that trying to move from a standing start on an incline on the biggest ring front and rear exerts the most force - which is nonsensical!

As I said there are too many variables - rider weight for example?

...and I think you're mistaking the amount a force required to create a mechanical advantage with the ratio of the gears being used;

With the chain on the biggest ring at the front you actually have a 'longer lever' with which to pull the chain round the rear cog but you would have to exert far more force than is possible to achieve the same result...

Hoiking up hill on the Granny ring doesn't necessarily apply any more force to the chain than doing the same on a gentler incline on the middle ring, or standing up to sprint on the big ring of a road bike - even for riders of equal weight...

 

[Unclejack]

would not the following apply?

 

[WD Pro]

My way of thinking :

With the back wheel locked / bolted to the floor, the smallest chain wheel would provide the highest chain tension - but that doesn’t happen.

Powerful cars break stuff when they hook up / get traction.

400 hp with a crap geometry and nankang 135 section ditch finders aint going to break nowt (within reason) or make good use of its power / torque - it's only good if you can actually use it.

So ...

Based on OFF ROAD - can we really use all that torque that standing on the pedals in the lowest chain wheel can provide ? I guess not as you will either be quickly at a speed where you can’t stand on the pedals anymore or you will have lost traction ...

Based on ON ROAD - with a steep enough hill and no wheel slip I guess the theory of smallest chain wheel / highest chain tension would prove true in those situations where cadence is low and you are standing on one pedal and pulling on the other.

It would be interesting to start a poll – When did you break your chain ? including options with a combination of - big chain wheel / small chain wheel / on road / off road / low cadence / high cadence etc

In reality I would suspect (guess ) that most chains have broken under conditions giving good traction in higher gears (then you should be in) but at lower cadences ?

WD