Chain sizing - going from L to M cage deraileur- Mtbr.com
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  1. #1
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    Chain sizing - going from L to M cage deraileur

    I am rebuilding a bike into a 1x, and just replaced the rear derailleur from L to M cage. Everything I've read on chain sizing has you get the measurement before running it through the derailleur. Having trouble getting my head around how the cage length doesnt affect the chain length. Can anyone explain this to me -- been reading online but cant find this aspect addressed. Thank you.
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  2. #2
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    I have thought this also... I don't think it's addressed because its only about a 2 link difference.. the long rear der. would only need a link or two more... chain length isn't really rocket science.. you just want to make sure the big ring/big cog isn't pulling that rear der. too much forward..

    I am of the philosophy that the shorter the chain the better and you don't want that rear der. looking awkwardly stretched forward on the big/big...

    Its not rocket science

  3. #3
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    It does but it's so minor

  4. #4
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    Size it based on the big/big combo to ensure you're not stretching out that rear der.....that's it.




  5. #5
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    Easy to take more links out... Hard to put them back in.
    "You either want to or you don't."

  6. #6
    PMP,TAN,LAUNDRY
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    I asked this question when I went from a 32 to 30 chainring. I know it's a little different question because of the derailleur but it made no difference. I received a good explanation in the Santa Cruz forum but not sure if I can find it.
    Bender to AZDog: I'm not the best person to give advice on not riding!

  7. #7
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    What cassette are you running? If you are running a 42T you may want to run an extra two links from the traditional set up of big-big +2 links.
    AKA: G-wat

  8. #8
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    thanks for the feedback everyone. Except you AZdog - you are a *****y little tease.

    JIC anyone wants to learn, I strung it through and everything seems darn near unchanged. *headscratch*. guess i should just ride!
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  9. #9
    PMP,TAN,LAUNDRY
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    Found it:

    "Every 4 teeth you go up or down equals 1" in chain added or removed (one pair of links).
    So 2 teeth difference would mean 1/2" less chain optimally.

    So you are probably good, change your chainring and look at the position of the derailleur in the highest and lowest gears. And then pull the chain together to simulate less chain and see if its gets too close to the end range of the derailleur".
    Bender to AZDog: I'm not the best person to give advice on not riding!

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