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Videos of noisy rear cog

Old 05-16-15, 09:20 PM
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Inpd
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Videos of noisy rear cog

Hi,

So as your an see it gets noisy on the smaller cogs. Is this a problem? If it is, is the cog or chain or dereilluer the issue.

https://www.dropbox.com/s/vpl2y0dqzzcnlpz/img_1869.mov?dl=0 https://www.dropbox.com/s/lwop7jj05d6ewv9/img_1870.mov?dl=0
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Old 05-17-15, 06:19 AM
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alcjphil
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One of the reasons why small cogs are noisier is that they are not truly round. This is also true with larger cogs but the effect is less. 11 tooth cogs are particularly bad in this respect. Another reason small cogs are noisier is that there are fewer teeth engaged with the chain so each cog carries a bigger load. Even with minimal chain stretch, when the chain disengages from the last cog as you pedal there will be some noise. If you use the smallest cog frequently, it will wear much faster than a bigger one, and if you hardly ever use it, it will be much less worn than the others that you use all the time. Depending on how you ride, certain cogs in all cassettes wear faster than others which is why when you install a new chain and notice that it slips it will only be in one or two gears
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Old 05-17-15, 06:39 AM
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Originally Posted by alcjphil View Post
One of the reasons why small cogs are noisier is that they are not truly round. This is also true with larger cogs but the effect is less. 11 tooth cogs are particularly bad in this respect. Another reason small cogs are noisier is that there are fewer teeth engaged with the chain so each cog carries a bigger load. Even with minimal chain stretch, when the chain disengages from the last cog as you pedal there will be some noise. If you use the smallest cog frequently, it will wear much faster than a bigger one, and if you hardly ever use it, it will be much less worn than the others that you use all the time. Depending on how you ride, certain cogs in all cassettes wear faster than others which is why when you install a new chain and notice that it slips it will only be in one or two gears
Thanks you for your detailed explanation. I should have been more clearer, the noise also occurs on the other cogs just not as much. The bike only has 600 miles on it.

Did you have a chance to look at the video? Is that noise normal? I alwayswonder with an entry level road bike if they skimped on some areas like chains and cogs.
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Old 05-17-15, 08:20 AM
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A common reason to have high cog noise but otherwise silent other cogs is that the high limit might be a tad too tight. Shimano road systems seem to be particularly sensitive to the high cog limit adjustment. I test for this by slightly pushing on the der towards the spokes or a slight tug on the cable, just enough to start the shifting but not enough to lift the chain. You can hear the difference between a well centered pulley, a slightly off center and the chain is JUST scuffing the next larger cog's side, and the chain almost being lifted up. Then pull the der outward and see how the sound changes. Andy.
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Old 05-17-15, 10:30 AM
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[QUOTE=alcjphil;17811893]One of the reasons why small cogs are noisier is that they are not truly round. This is also true with larger cogs but the effect is less. 11 tooth cogs are particularly bad in this respect. [/QUOTE:

This is known as "chordal action": 2.2.1 Chordal Action
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Old 05-17-15, 04:46 PM
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Inpd
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Originally Posted by Andrew R Stewart View Post
A common reason to have high cog noise but otherwise silent other cogs is that the high limit might be a tad too tight. Shimano road systems seem to be particularly sensitive to the high cog limit adjustment. I test for this by slightly pushing on the der towards the spokes or a slight tug on the cable, just enough to start the shifting but not enough to lift the chain. You can hear the difference between a well centered pulley, a slightly off center and the chain is JUST scuffing the next larger cog's side, and the chain almost being lifted up. Then pull the der outward and see how the sound changes. Andy.
Thanks Andy, Will definitely try this one.
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