Force in a chain?
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suburbanreuben
Old School Grand Master
There's only two different variables - The size of the front cog, and the size of the rear. What's tricky about that, apart from Friday night fuzzyhead?We_are_Stevo":36aercih said: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...
EDIT : the rear cog size is constant, so there's only one variable... :roll:
Have another go!
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Smallest cog has the potential to deliver an increased force into the chain, but what the rest of the system does does matter.
A chain has two forces acting on it one created by the chainset pulling the chain forward and one by the rear cogs and related pulling the chain back (which is equal to the force pulling the chain).
So you need to create a setup in the system where the max force the rider can provide, be it an impulse-ish force (quick set off by MTB) or a prolonged force (roadie large cogs accelerating) can be at a maximum.
in the real world MTB's do not need to push to hard in the low gears else the rear wheel looses traction. Hence why people are saying lock the rear wheel.
But assume the real wheel is stationary and cannot move. You apply the same force to the pedal at he front, then yes the small cog will deliver the largest force pulling the chain. More importantly as it has less teeth it applies a greater pressure at the tooth contact points as that force is shared out among less teeth.
So in the real world you're more likely to snap a chain in "24 front 12 rear" than "24 front 32 rear" as the 32 makes the bike move easier and so you have less time of the full force through the chain or may not actually achieve it as you have less to push against so you muscles not try as hard. Add on there is an increased pressure on the 12 tooth cog at the contact point*
of course the real-real world will not agree with this, as that's what it does best and many people don't try to set off in 24/12 so people do not notice it as much.
lost my train of thought now, damn children
*Yes it's also a bent chain on an mtb
A chain has two forces acting on it one created by the chainset pulling the chain forward and one by the rear cogs and related pulling the chain back (which is equal to the force pulling the chain).
So you need to create a setup in the system where the max force the rider can provide, be it an impulse-ish force (quick set off by MTB) or a prolonged force (roadie large cogs accelerating) can be at a maximum.
in the real world MTB's do not need to push to hard in the low gears else the rear wheel looses traction. Hence why people are saying lock the rear wheel.
But assume the real wheel is stationary and cannot move. You apply the same force to the pedal at he front, then yes the small cog will deliver the largest force pulling the chain. More importantly as it has less teeth it applies a greater pressure at the tooth contact points as that force is shared out among less teeth.
So in the real world you're more likely to snap a chain in "24 front 12 rear" than "24 front 32 rear" as the 32 makes the bike move easier and so you have less time of the full force through the chain or may not actually achieve it as you have less to push against so you muscles not try as hard. Add on there is an increased pressure on the 12 tooth cog at the contact point*
of course the real-real world will not agree with this, as that's what it does best and many people don't try to set off in 24/12 so people do not notice it as much.
lost my train of thought now, damn children
*Yes it's also a bent chain on an mtb
We_are_Stevo
Old School Grand Master
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Yey! Go Fluffy!
Another common sense reply...
For those of you who say there NOT too many variables try this;
Put your bike in the lowest gear, crouch down next to it and turn the pedal by hand - see how much effort it takes? Now lift the rear wheel off the ground and try it again; Easier huh? NOW have someone sit on the bike while you try to turn it by hand... :?
Now tell me rider weight doesn't make a difference!
As 'Fluffy Chicken' was leading up to above before he lost the will to live, the reason the chain is under the most tension to begin with is you are trying to overcome the 'resistance' of the drivetrain and the wheels contact with the ground. All the granny ring is doing is making it easier for you, the rider to apply enough effort to reach the point where you overcome that resistance. That point is going to be the same whatever hear you are in and the amount of force on the chain is going to be the same.
However, a lighter rider will reach that point before a heavier rider because there will be LESS resistance to overcome due to the lighter weight bearing down on the wheel.
Bleating on about the tension in the chain being highest in the granny ring is ignoring your own point; the chain will have a certain 'bursting point' when it will fail/snap - that bursting point is constant, it won't change. How you get to that point does...
Pulling away in the granny ring 'BRIEFLY' applies the greatest tension to the chain, but once you overcome the resistance and the bike starts to move then that tension falls - unless you change gear the chains rotation will get quicker and quicker intol the rear wheel is trying to push the chain forwards! If you try to pull away on the middle ring though you have to put more effort into it (because your lever is shorter) for longer, thus putting the same tension on the chain for longer and increasing that chance of failure. If you then suddenly apply more pressure in your effort to over come the resistance you increase the tension on the chain, with the equal and opposite effect of increasing the chance of failure...
Another common sense reply...
For those of you who say there NOT too many variables try this;
Put your bike in the lowest gear, crouch down next to it and turn the pedal by hand - see how much effort it takes? Now lift the rear wheel off the ground and try it again; Easier huh? NOW have someone sit on the bike while you try to turn it by hand... :?
Now tell me rider weight doesn't make a difference!
As 'Fluffy Chicken' was leading up to above before he lost the will to live, the reason the chain is under the most tension to begin with is you are trying to overcome the 'resistance' of the drivetrain and the wheels contact with the ground. All the granny ring is doing is making it easier for you, the rider to apply enough effort to reach the point where you overcome that resistance. That point is going to be the same whatever hear you are in and the amount of force on the chain is going to be the same.
However, a lighter rider will reach that point before a heavier rider because there will be LESS resistance to overcome due to the lighter weight bearing down on the wheel.
Bleating on about the tension in the chain being highest in the granny ring is ignoring your own point; the chain will have a certain 'bursting point' when it will fail/snap - that bursting point is constant, it won't change. How you get to that point does...
Pulling away in the granny ring 'BRIEFLY' applies the greatest tension to the chain, but once you overcome the resistance and the bike starts to move then that tension falls - unless you change gear the chains rotation will get quicker and quicker intol the rear wheel is trying to push the chain forwards! If you try to pull away on the middle ring though you have to put more effort into it (because your lever is shorter) for longer, thus putting the same tension on the chain for longer and increasing that chance of failure. If you then suddenly apply more pressure in your effort to over come the resistance you increase the tension on the chain, with the equal and opposite effect of increasing the chance of failure...
We_are_Stevo
Old School Grand Master
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You'll have to excuse the random typo's - I sent that from my mobile and I have big thumbs!
suburbanreuben
Old School Grand Master
We_are_Stevo":thtkoegr said:Yey! Go Fluffy!
Another common sense reply...
For those of you who say there NOT too many variables try this;
Put your bike in the lowest gear, crouch down next to it and turn the pedal by hand - see how much effort it takes? Now lift the rear wheel off the ground and try it again; Easier huh? NOW have someone sit on the bike while you try to turn it by hand... :?
Now tell me rider weight doesn't make a difference!
As 'Fluffy Chicken' was leading up to above before he lost the will to live, the reason the chain is under the most tension to begin with is you are trying to overcome the 'resistance' of the drivetrain and the wheels contact with the ground. All the granny ring is doing is making it easier for you, the rider to apply enough effort to reach the point where you overcome that resistance. That point is going to be the same whatever hear you are in and the amount of force on the chain is going to be the same.
However, a lighter rider will reach that point before a heavier rider because there will be LESS resistance to overcome due to the lighter weight bearing down on the wheel.
Bleating on about the tension in the chain being highest in the granny ring is ignoring your own point; the chain will have a certain 'bursting point' when it will fail/snap - that bursting point is constant, it won't change. How you get to that point does...
Pulling away in the granny ring 'BRIEFLY' applies the greatest tension to the chain, but once you overcome the resistance and the bike starts to move then that tension falls - unless you change gear the chains rotation will get quicker and quicker intol the rear wheel is trying to push the chain forwards! If you try to pull away on the middle ring though you have to put more effort into it (because your lever is shorter) for longer, thus putting the same tension on the chain for longer and increasing that chance of failure. If you then suddenly apply more pressure in your effort to over come the resistance you increase the tension on the chain, with the equal and opposite effect of increasing the chance of failure...
Ho hum... :roll:
Reading some of these theories, I'm seriously worried about the future of mankind...
Here goes:
Everything is constant except cog sizes, OK?
Let's assume we double the ratio between front and back cogs, from 2:1 to 4:1, eg 32:16 to 64:16.
We could acheive the same thing by making the rear cog smaller, 32:16 becomes 32:8.
Ya with me at the back?
Tor simplify matters, assume the 16 rear cog is twice the diameter of the 8 cog (it isn't, but humour me).
Therefore, to exert the same rotational force on tyre/ ground contact point requires half the force at the chain/sprocket point because the lever for the 16 t cog is twice as long as the 8t cog.
Still with me?
If the force at the 8t cog is twice that at the 16tcog, then the force in the chain ,must also be twice as strong with the smaller cog, imp,lying the rider needs to exert twice the power with the small cog.
This is why we need to put in "more effort" with a large front/small rear setup.
More effort required means more stress (force) on the components, including the chain (especially the chain!).
Bored yet?
Yeah, so am I...
suburbanreuben
Old School Grand Master
suburbanreuben
Old School Grand Master
The tension in the chain in these examples wiould be the same...JamesM":1r6ppzqj said:
We_are_Stevo":2ep7g5lp said:Yey! Go Fluffy!
Another common sense reply...
For those of you who say there NOT too many variables try this;
Put your bike in the lowest gear, crouch down next to it and turn the pedal by hand - see how much effort it takes? Now lift the rear wheel off the ground and try it again; Easier huh? NOW have someone sit on the bike while you try to turn it by hand... :?
Now tell me rider weight doesn't make a difference!
.... but that is irrelevant.
when you are exerting maximum torque/force, you can be doing that when stationary or when moving - the rear gear and riders weight make no difference - as either you are at maximum or not.
As far as your legs can feel/tell - they don't know if the resistance is due to a steep hill or the back wheel bolted to the ground.
yes , the gearing and riders weight will determine under what circumstatnces you will be pushing at your max but once you are at your max, as I keep saying, the length of crank and diameter of front chain wheel is all that matters for determining the max force pulling on the chain.
