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  1. #1
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    new chain old cog

    would a new chain and old cog make a lot of noise? i am experienceing this now. the cog is quite old with tons and tons of miles on it. its not a constant noise though, its only when i push down. if i put no pressure, not a sound.
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    cyclist/gearhead/cycli... moxfyre's Avatar
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    Yeah, that's quite common. If you let a cog and chain wear out together, then replace the chain without replacing the cog (or vice versa), you're likely to have skipping or excess noise, and you'll wear out the new chain very quickly.

    Read Sheldon Brown's excellent article on chain wear: www.sheldonbrown.com/chains.html#wear ... basically chain and sprocket wear contibute to each other in a vicious cycle, so it's important to clean and/or replace the chain frequently if you don't want to wear out your cogs!
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  3. #3
    ride, paint, ride simplify's Avatar
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    Yeah, it sure could do that. If your chainring is so worn that the profile of the teeth has changed, then it won't mesh quite right with the new chain. That won't harm the new chain, but can be noisy, and in extreme cases, might skip. Same is true of rear cogs that are worn. They don't mesh well with the new chain, might be noisy, and could even cause the chain to skip.
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  4. #4
    ride, paint, ride simplify's Avatar
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    Whoa! Does it wear out the chain faster? I always thought that a new chain isn't affected much by worn cogs or chainrings (other than aesthetically), whereas a worn chain will definitely wear out cogs and chainrings faster.
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    cyclist/gearhead/cycli... moxfyre's Avatar
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    Quote Originally Posted by lawkd
    Whoa! Does it wear out the chain faster? I always thought that a new chain isn't affected much by worn cogs or chainrings (other than aesthetically), whereas a worn chain will definitely wear out cogs and chainrings faster.
    Yeah, unfortunately it goes both ways... If you have worn cogs and put on a new chain, the stress from the sprockets won't be spread among the chain rollers, but instead concentrated on a single roller at a time. This will cause faster chain wear. Sheldon describes it much better than me

    I can definitely say that when I put a new chain on sprockets where the previous chain was worn past the 1/2% mark, the new chain wore out faster.
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    me have long head tube TallRider's Avatar
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    I'm actually pretty sure that it doesn't work both ways - or at least not both ways equally. In my understanding, a worn chain can wear out new cogs, but worn cogs won't wear out a new chain. At the very least there's less danger of worn cogs or chainrings wearing out a new chain. Here's why:
    * A worn chain is elongated. This means that most of the force exerted by chain on cogs or by chainrings on the chain is transferred through one or a few gear teeth. This causes the teeth to wear much more quickly than if the force was transmitted along a larger number of teeth. (It's also the same reason that 11t cogs wear out quickly if you use them regularly - even a new chain isn't in contact with very many teeth. Fortunately most riders who have an 11t cog don't use it much.)
    * A worn cog or chainring has its teeth in a shark-fin shape. However, the teeth are still the same distance apart as they were before, and so force on the chain is relatively equally-distributed on the chain links even from worn teeth. Moreover, even if force isn't as equally distributed among chain links, the chain isn't directly disadvantaged by this to the degree that chainring teeth are.

    For very-worn cogs or chainring teeth, there is some danger of wearing out a new chain. This is because more shark-finned teeth contact the chain roller at an angle that forces the chain up and away from the center of the cog or chainring's rotational axis (again, this is more pronounced on smaller cogs/chainrings with fewer teeth, because there is more curvature per tooth). The further away the chain is pushed from the cog or chainring's axis of rotation (and for a given amount of tooth wear, this is inversely proportional to the number of teeth in the chainring or cog because more teeth equals less curvature per tooth) the further the distance between the teeth. So worn cogs are more of a danger to wear out new chains than are worn chainrings.
    This forcing-the-chain-up usually causes the chain to skip. One reason why, practically-speaking, you should be able to ride a cog without worrying how it's going to affect your chain, so long as the chain doesn't skip.

  7. #7
    cyclist/gearhead/cycli... moxfyre's Avatar
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    Quote Originally Posted by timcupery
    I'm actually pretty sure that it doesn't work both ways - or at least not both ways equally. In my understanding, a worn chain can wear out new cogs, but worn cogs won't wear out a new chain. At the very least there's less danger of worn cogs or chainrings wearing out a new chain.
    Tim, a worn sprocket effectively has a different pitch from a new one, since the chain has worn a sort of curved ramp into the sprocket. Sheldon Brown's article explains how that works. I don't know if the two proceed at the same rate, you may well be right about that.

    The bigger problem than wearing out the new part quickly is that a new chain will very likely skip/slip on old sprockets. This is extremely annoying... I hate it when I put on a new chain and then mash hard and the chain is flying off the sprockets all over the place.
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    me have long head tube TallRider's Avatar
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    Sorry, you're right that the pitch or a worn cog is changed, but it's only changed because the shark-finned ramped shape of worn teeth forces the chain further away from the axis of the cog or chainring, thus increasing the distance needed to wrap a given number of teeth on the cog, exerting force on the chain to lengthen it. I'd figured that out in the second part of my post above, but should have gone back and changed the first post.

    This mechanism also explains why larger cogs (let alone chainrings) are less likely to pose a problem either for skipping or wearing out a new chain.

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    cyclist/gearhead/cycli... moxfyre's Avatar
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    Quote Originally Posted by timcupery
    This mechanism also explains why larger cogs (let alone chainrings) are less likely to pose a problem either for skipping or wearing out a new chain.
    Yeah. I also think that it's because larger cogs have more teeth to spread the WEAR, have more teeth to spread the LOAD (the same teeth, of course ), get used less by most riders (I think), and don't bend the chain at as sharp an angle. I'm sure the interplay of all these factors is quite complex!
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  10. #10
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    Fascinating. But don't you think that a new chain could--and would--simply stay near the bottom of those ramps that were created by the former stretched chain, and do its work there? Maybe there would be an inclination for the chain to go up the ramps, but each link *could* stay at the lower end of the ramp and exert its force against the cog there...
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  11. #11
    cyclist/gearhead/cycli... moxfyre's Avatar
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    Quote Originally Posted by lawkd
    Fascinating. But don't you think that a new chain could--and would--simply stay near the bottom of those ramps that were created by the former stretched chain, and do its work there? Maybe there would be an inclination for the chain to go up the ramps, but each link *could* stay at the lower end of the ramp and exert its force against the cog there...
    Well... I'm not sure why it doesn't do that, but it seems that's not always the case. If the rollers of a new chain could just stay at the lower ends of the ramp, and spread out the force among multiple links, why would new chains slip on old cogs? It seems like there's something that must prevent that from happening, forcing a single link to bear the load and causing it to slip.
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  12. #12
    ride, paint, ride simplify's Avatar
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    Excellent point and food for thought. You know, this brings up one more reason why I love the old Uniglide twist-tooth cogs from Shimano. They were so much taller than the current sawed-off Hyperglide stuff, so the impression from the chain made a sort of little indentation which wouldn't let the chain slip up to the top and skip. I personally haven't heard of a Uniglide cog skipping, even under load, even when very worn. I'm sure it's happened, but it's at least much less common than on the newer cogs--which are also thinner, therefore wear out faster.

    I'm starting to sound like an old curmudgeon.
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    cyclist/gearhead/cycli... moxfyre's Avatar
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    Quote Originally Posted by lawkd
    Excellent point and food for thought. You know, this brings up one more reason why I love the old Uniglide twist-tooth cogs from Shimano. They were so much taller than the current sawed-off Hyperglide stuff, so the impression from the chain made a sort of little indentation which wouldn't let the chain slip up to the top and skip. I personally haven't heard of a Uniglide cog skipping, even under load, even when very worn. I'm sure it's happened, but it's at least much less common than on the newer cogs--which are also thinner, therefore wear out faster.

    I'm starting to sound like an old curmudgeon.
    Nah, you usually sound like the voice of reason!

    I too like the durability of the old stuff (Suntour freewheels anyone?). Newer cassettes wear out so fast it's downright frustrating. You wouldn't think that wearing out your chain to 1% elongation would cause all 3 smallest cogs to skip, but that's what happened to me recently on my 8-speed hyperglide cassette.

    The big advantage of the newer cassettes is the shift ramps, which in my opinion make a huge difference. People think index shifting makes a bike so much easier, but it's mostly the shift ramps I think. With Hyperglide cogs friction shifting is a breeze for me. I wish there were thicker cogs with shift ramps. A cassette is a stupid place to try and save 100 g for most riders.

    PS- I've been using Nashbar cassettes for a few months, which feature good shift ramps, but they are heavier than the Shimano cassettes. I mic'd the cogs and they are thicker than the 1.8 mm 8-speed hyperglide cogs. Don't know yet how much more durable they will be, but I'm hopeful...
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  14. #14
    me have long head tube TallRider's Avatar
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    sorry I've been away for awhile. (well, actually not something I need to apologize for.) Here's some responses.

    Quote Originally Posted by moxfyre
    Yeah. I also think that it's because larger cogs have more teeth to spread the WEAR, have more teeth to spread the LOAD (the same teeth, of course ), get used less by most riders (I think), and don't bend the chain at as sharp an angle. I'm sure the interplay of all these factors is quite complex!
    Yeah, larger cogs/chainrings wear less quickly because there's more teeth to go around. But for a given amount of wear (e.g., amount of shark-finning of the teeth), a smaller cog will exert more chain-wearing/stretching force on a new chain than will a large cog. That's because the mechanism of worn teeth stretching a new chain is that the tooth contacts the chain roller at an angle which exerts force outward as well as forward on the chain. the outward component of that force is pushing the chain away from the axis of the cog or chainring. A larger circle is also further around. That is, if a chain roller is pushed 1mm outward away from the axis of the chainring or cog, the teeth are effectively further apart. Hence the wear on your chain.
    But with smaller cogs/chainrings, the pitch of the teeth increases more quickly for a given increase in distance from the axis of the cog/chainring, because the proportional distance increases more quickly, because the starting distance is smaller.

    Quote Originally Posted by lawkd
    Fascinating. But don't you think that a new chain could--and would--simply stay near the bottom of those ramps that were created by the former stretched chain, and do its work there? Maybe there would be an inclination for the chain to go up the ramps, but each link *could* stay at the lower end of the ramp and exert its force against the cog there...
    The reason that the chain won't just stay at the bottom is because of the angle at which chainring teeth contact the chain roller. More worn teeth are more angled away from vertical, so a greater percentage of the force that they transmit to the chain roller is outward from the cog or chainring and not tangent.

    Quote Originally Posted by lawkd
    [snip] this brings up one more reason why I love the old Uniglide twist-tooth cogs from Shimano. They were so much taller than the current sawed-off Hyperglide stuff, so the impression from the chain made a sort of little indentation which wouldn't let the chain slip up to the top and skip. I personally haven't heard of a Uniglide cog skipping, even under load, even when very worn. I'm sure it's happened, but it's at least much less common than on the newer cogs--which are also thinner, therefore wear out faster.
    I've seen Uniglidde cogs get worn out and skip. But I suspect that they are more durable because the teeth are higher - more steel needs to get worn away before they are shark-finned. On the other side, the higher teeth also made them less likely to skip when worn... but it also meant that shifts from one cog to another were less quick and responsive.

  15. #15
    cyclist/gearhead/cycli... moxfyre's Avatar
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    Quote Originally Posted by timcupery
    sorry I've been away for awhile. (well, actually not something I need to apologize for.) Here's some responses.
    Shame on you for doing something besides bikeforums

    Yeah, larger cogs/chainrings wear less quickly because there's more teeth to go around. But for a given amount of wear (e.g., amount of shark-finning of the teeth), a smaller cog will exert more chain-wearing/stretching force on a new chain than will a large cog. That's because the mechanism of worn teeth stretching a new chain is that the tooth contacts the chain roller at an angle which exerts force outward as well as forward on the chain. the outward component of that force is pushing the chain away from the axis of the cog or chainring. A larger circle is also further around. That is, if a chain roller is pushed 1mm outward away from the axis of the chainring or cog, the teeth are effectively further apart. Hence the wear on your chain.
    But with smaller cogs/chainrings, the pitch of the teeth increases more quickly for a given increase in distance from the axis of the cog/chainring, because the proportional distance increases more quickly, because the starting distance is smaller.


    The reason that the chain won't just stay at the bottom is because of the angle at which chainring teeth contact the chain roller. More worn teeth are more angled away from vertical, so a greater percentage of the force that they transmit to the chain roller is outward from the cog or chainring and not tangent.
    Yeah, I think that's a very good explanation of why the chain won't stay at the bottom.

    As for wearing out the *chain*, I think you've got a really interesting idea about the tangential vs. radial force. If I understand what you're saying correctly, the curvature of a sprocket tooth pushes the chain roller radially, while the tension from the rest of the chain applies tangential forces. From your explanation, it follows that smaller cogs will apply greater radial force, which might result in faster chain wear.

    You might want to run that by Sheldon Brown, it seems like the kind of thing he would put on his pages!

    I've seen Uniglidde cogs get worn out and skip. But I suspect that they are more durable because the teeth are higher - more steel needs to get worn away before they are shark-finned. On the other side, the higher teeth also made them less likely to skip when worn... but it also meant that shifts from one cog to another were less quick and responsive.
    I think the cog width has to play a role here as well (as lawkd suggested). The wider the cog, the greater the area over which the sprocket tooth supports the force applied by the chain roller. Thus, there should be a proportionally lower pressure on wider cog teeth, given equal chain tension.

    I don't know the exact mechanism by which the metal wears off the teeth, but I suspect that it is strongly dependent on the pressure (as is this case in most other abrasive processes, e.g. sanding a block of wood).
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    me have long head tube TallRider's Avatar
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    I'm still trying to figure out if the radial force of worn teeth on teh sprocket increases wear simply because it adds to the maximum force on the chain - by about a factor of 1.4 in a severely worn cog - or if the pushing the chain outward not only increases maximum force but localizes forces on a smaller number of chain links. Not sure on this. thoughts?

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    cyclist/gearhead/cycli... moxfyre's Avatar
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    Quote Originally Posted by timcupery
    I'm still trying to figure out if the radial force of worn teeth on teh sprocket increases wear simply because it adds to the maximum force on the chain - by about a factor of 1.4 in a severely worn cog - or if the pushing the chain outward not only increases maximum force but localizes forces on a smaller number of chain links. Not sure on this. thoughts?
    Hmmm... I don't think it will localize the force on fewer chain links, simply because the sprocket should wear symmetrically. The way I'm picturing it is a sprocket with a chain wrapped around it, but the chain rollers are "riding up" on the teeth rather than sitting in the valleys between the teeth.

    How'd you come up with the factor of 1.4 for the increased force on the rollers?
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    Quote Originally Posted by moxfyre
    Hmmm... I don't think it will localize the force on fewer chain links, simply because the sprocket should wear symmetrically. The way I'm picturing it is a sprocket with a chain wrapped around it, but the chain rollers are "riding up" on the teeth rather than sitting in the valleys between the teeth.
    How'd you come up with the factor of 1.4 for the increased force on the rollers?
    1.4 = a little less than the square root of 2. For a given force applied directly in tangential plane, the same amount of tangential force applied by a tooth at a 45 degree angle will end up being a total force (tangential + radial planes) of 1.414 times the value of the tangential-plane force.

    But I think you're right in that the force won't be localized over fewer chain links. If the chain is stretched byt the cogs aren't worn, force is localized over individual cogs. But with worn cogs causing a new unstretched chain to "ride up" the force will be very much distributed among all the teeth. So it really is just the extra force caused by the teeth contacting the chain rollers at more of an angle.

    Here's a good picture illustrating the shark-fin wearing of teeth. The granny ring off my brother's road bike that he road for thousands of miles without changing (or much servicing) the chain. Even this the teeth aren't worn to 45 degrees, so the total force would be more like 1.25 or 1.3 times that of an unworn tooth (which isn't perfectly vertical in its contact anyway, although not far from vertical).

  19. #19
    cyclist/gearhead/cycli... moxfyre's Avatar
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    Quote Originally Posted by timcupery
    1.4 = a little less than the square root of 2. For a given force applied directly in tangential plane, the same amount of tangential force applied by a tooth at a 45 degree angle will end up being a total force (tangential + radial planes) of 1.414 times the value of the tangential-plane force.
    There's something oddly unintuitive about that, like some conservation law is being violated, but I can't find fault with the math

    If the chain tension is unchanged, the tangential force on each individual roller ought to be Tension / (# teeth engaged). And it makes sense that more total force must be applied to achieve a given tangential force at a steeper angle. I suppose it's like trying to push a door closed by applying a force perpendicular to the door, versus applying a glancing force. Yep, makes sense.

    But I think you're right in that the force won't be localized over fewer chain links. If the chain is stretched byt the cogs aren't worn, force is localized over individual cogs. But with worn cogs causing a new unstretched chain to "ride up" the force will be very much distributed among all the teeth. So it really is just the extra force caused by the teeth contacting the chain rollers at more of an angle.
    Actually, now that I re-read Sheldon Brown's explanation, it seems like your original intuition was correct: the teeth at the "entering" side of the sprocket are engaging the chain properly, while the teeth at the "exiting" side are riding up and not applying as much force to the chain.

    Of course, this all assumes that you and Sheldon Brown are both correct in the part of the phenomenon that you're describing. Aren't you supposed to be a frickin' sociology major?

    Here's a good picture illustrating the shark-fin wearing of teeth. The granny ring off my brother's road bike that he road for thousands of miles without changing (or much servicing) the chain. Even this the teeth aren't worn to 45 degrees, so the total force would be more like 1.25 or 1.3 times that of an unworn tooth (which isn't perfectly vertical in its contact anyway, although not far from vertical).
    Wow, that's a bad one!
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    Quote Originally Posted by moxfyre
    Of course, this all assumes that you and Sheldon Brown are both correct in the part of the phenomenon that you're describing. Aren't you supposed to be a frickin' sociology major?
    Yeah, but I aced all of my physics, math and engineering classes for the first two years of college before I settled on studying people as more interesting. I took some classes in physiology and biomechanics and tested prototype running shoes for Adidas all the way through college, as well as a couple of times for Mizuno and Nike. I'm pretty confident in my ability to mentally model basic Newtonian-mechanical systems. Sadly enough, this knowledge is wasted on sociologists and doesn't impress them.

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    Quote Originally Posted by timcupery
    Yeah, but I aced all of my physics, math and engineering classes for the first two years of college before I settled on studying people as more interesting. I took some classes in physiology and biomechanics and tested prototype running shoes for Adidas all the way through college, as well as a couple of times for Mizuno and Nike. I'm pretty confident in my ability to mentally model basic Newtonian-mechanical systems. Sadly enough, this knowledge is wasted on sociologists and doesn't impress them.
    Yeah, well... well... I was a double major in linguistics as an undergrad. I can, uh, figure out etymology quickly, draw syntax trees, and speak French and Spanish well. Actually it's not so bad, I had a very good job at a speech synthesis company for a while, which perfectly combined my interests in physics and linguistics (it was like a miracle job for me, really ).

    You seem to be the one of the resident "scientific reality" guys here, always ready to throw in an equation here or there when the claims of component performance or comfort get a little too fantastical! Good work. Testing running shoes sounds pretty cool, I guess you got that gig as a cross-country runner?
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    Quote Originally Posted by moxfyre
    You seem to be the one of the resident "scientific reality" guys here, always ready to throw in an equation here or there when the claims of component performance or comfort get a little too fantastical! Good work. Testing running shoes sounds pretty cool, I guess you got that gig as a cross-country runner?
    Yeah, I ran cross-country in college. Back then I was a guru on Runner's World's shoe forums, which is what initially got me connected to Adidas.

    Btw, I certainly know of your grandfather - and still think quite highly of his work on Human Societies, and on the study of religion.
    Last edited by TallRider; 09-26-06 at 10:44 PM.

  23. #23
    cyclist/gearhead/cycli... moxfyre's Avatar
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    Quote Originally Posted by timcupery
    Yeah, I ran cross-country in college. Back then I was a guru on Runner's World's shoe forums, which is what initially got me connected to Adidas.
    Yeah, I think you mentioned that. Sounds like a cool job! Now you have to get it for bikes, there's a lot more expensive equipment to get free samples of. "Hi, this is Tim. I didn't quite get a good feel for that carbon crankset before I destroyed it. Can you send me another?"

    Btw, I certainly know of your grandfather - and still think quite highly of his work on Human Societies, and on the study of religion.
    Cool! I'll give him a shout-out for you He emailed me today so I ought to write back. I've read a few chapters of his books, particularly one on Ancient Israel which I am very interested in.
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    Sheldon Brown, I miss you. Thanks for the advice, ideas, humor, and infectious enthusiasm for everything bikes...

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