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  1. #1
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    Chain issue after cog swap

    I had my rear cog changed over at my LBS on my 2011 Trek Rig. It went from 32/18 to 32/20. I was surprised when the guy in shop said he didn't need to take a link out. I got the impression he had tried but it didn't quite work. Anyhow, the first ride afterwards on a bit of a strenuous climb I felt the chain pull or ratchet momentarily. ....it's hard to explain. Anyway, the result was the the chain looked like this:



    I loosened rear left and right bolts (etc) and recessed them back thus tightening the chain and it looked really good and a test ride or two it was fine, Yet the same thing has happened another strange noise and a slackness has appeared (albeit this time only half as bad).

    Whats going on here? I'm fairly sure all of the bolts are really quite tight. Should I try and remove a link??

  2. #2
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    If you change a cog you should also change your chain. What happens is from pedalling hard your chain gets stretched (that's why your LBS didn't have to ADD 2 links when going from 18 to 20). Then when you use a new cog the chain is longer than the opening between the teeth on your cog, and your chain starts slipping. Now if you put more tension on your chain then it can no longer slip but it will make a cracking noise as the chain is forced onto the cog.
    My advice (FWIW) just change your chain and it'll be fine. If you can , use a Sram PC1, it's a bit wider (1/8" instead of 3/32" 9-speed) and thus a bit stronger. But it will still stretch though.

  3. #3
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    Thanks for that, I will try that.

    Should I try and revert the bolt positions to the stock setting at same time, or that's no biggie?

    Quote Originally Posted by dmx1 View Post
    If you change a cog you should also change your chain. What happens is from pedalling hard your chain gets stretched (that's why your LBS didn't have to ADD 2 links when going from 18 to 20). Then when you use a new cog the chain is longer than the opening between the teeth on your cog, and your chain starts slipping. Now if you put more tension on your chain then it can no longer slip but it will make a cracking noise as the chain is forced onto the cog.
    My advice (FWIW) just change your chain and it'll be fine. If you can , use a Sram PC1, it's a bit wider (1/8" instead of 3/32" 9-speed) and thus a bit stronger. But it will still stretch though.

  4. #4
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    Don't worry about bolt position. Just make sure that your chain has enough tension but not too much. You should be able to lift the chain with your finger 1.5 times it's height.

  5. #5
    one chain loop
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    looking at your rear skewer, it seems like your wheels is just about ready to slide out of your dropout too. i think that's why your chain is too loose.

    re-mount your wheel and tighten that skewer.
    everything sucks but my vacuum cleaner.

  6. #6
    one chain loop
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    check this thread while you are at it:

    Trek Rig rear wheel falling out: diagnosis and solution
    everything sucks but my vacuum cleaner.

  7. #7
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    thanks for all of your replies.

    In the end I got an Outland half link chain and re-tensioned all necessary bits. seems to have industrial strength


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