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  1. #1
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    Question about determining chain length

    I have read from several different sources on to determine the chain length: Put the open chain on the largest cogs front and back, without the derailleurs, without slack, and add a link.

    I'm having trouble wrapping my mind around this concept--how would the chain be long enough using this method? After the derailleurs are added, how would the chain be long enough if/when one chooses to put the chain on the biggest cogs front and back?

    Also, presuming the above method is correct, does "no slack" mean pull the chain taut?

    Thanks.

  2. #2
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    its more like an inch (2 links), but it works. try it and you'll see, and you'll wonder why you doubted yourself.

    and yes, no slack = pull chain taut.

  3. #3
    local trails rider
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    Quote Originally Posted by brillantesdv
    its more like an inch (2 links),
    Depends on your definition of a "link". Many take one link to mean a narrow piece and a wide piece together.

    -------
    Rear suspension tends to complicate this: the distance from BB to rear axle rarely remains constant throughout the suspension cycle.

    But the principle is: you need to have just enough chain, in case you should ever shift to the large-large combination (not recommended but it happens).

    If you have much more chain than you need, the chain gets too slack in the smaller combinations.

  4. #4
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    The "definition" of a link is both pieces.....the space between 3 rivets. Always has been.

    That advice is standard and it works. It's based on road bikes and hardtails, however. Most suspension designs are fine with it, too, but some want an extra link in order to prevent ghost shifting or wrapping up the rear derailleur and ripping it off the knuckle. Depends on the rear wheel path....if it grows a little bit then you need an extra link in there. VPP is a good example of this.

    The derailleur's "other" job is to take up slack in the chain with the cage length via spring tension. When you cut your chain to length this way, you're allowing just enough to cover the big-big combination....the derailleur will do the rest. Since you should never really be riding your gears in that combo, the chain won't be too short in normal gearing combos and you've allowed for the worst case scenario. If you're in the big-big, the derailleur will be stretched out to the max and maybe get a little noisy, but it won't harm anything. Make sense?

  5. #5
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    Thank you guys. I appreciate all the information. I do need to remember to fully compress the suspension when measuring. While recognizing that big-big is not a typical nor recommended combination, I was having troble seeing how having "just long enough" plus the "space of 3 rivets" gives one enough length to run the chain through the rear derailleur (with the big-big).

    I believe that it works, but I'm just having trouble visualizing it.

    Thanks again guys.

  6. #6
    local trails rider
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    In the big-big combination, the derailer ends up pointing almost straight forward (or it should). The bends in the chain, through it, are relatively gentle in that position.

  7. #7
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    So does this method work for a hammerschmidt x 9 speed cassette (11-34) combo as well where there is no big-big?

  8. #8
    ~Disc~Golf~
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    Quote Originally Posted by handsomedan
    So does this method work for a hammerschmidt x 9 speed cassette (11-34) combo as well where there is no big-big?
    yep - the hammerschmidt is one of the 'bigs' even though it's small
    Honestly... ahh I give up

  9. #9
    keeping it dirty
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    That video makes it seem like this should only be done with SRAM rear derailleur and chain

  10. #10
    ~Disc~Golf~
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    Quote Originally Posted by intoflatlines
    That video makes it seem like this should only be done with SRAM rear derailleur and chain
    And with a Sette Flite!
    Honestly... ahh I give up

  11. #11
    keeping it dirty
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    ok ok you got me

  12. #12
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    i guess it seems like an extra inch of chain/2 links won't be enough length to get it through the derailleur when i'm in the 34 tooth cog and still have a nice S shape http://www.parktool.com/repair/readhowto.asp?id=26. when you have the big-big measurement i assumed that nobody is using the big-big combination while riding giving them enough chain length to avoid killing their rear derailleur. anyway i'll give it a try.

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