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  1. #1
    mtbr member
    Join Date
    May 2011

    Does Direct Mount RD affect chain length?

    I need a new derailleur hanger for my Mojo HD and think I might as well go with the direct mount. I'm running 2x10 with a short cage xtr shadow plus rear derailleur. Needless to say, I have a very specific chain length in order to make this work. If I switch to a direct mount hanger, will my perfect chain length get thrown off?

    My understanding is that I can remove the "B link" on my RD and that it will only work if the B Link has an allen head bolt, not torx. Can anyone verify that?

    Anyone already running the direct mount? Any actual differences? Looks clean and simple. B link seems superfluous.

  2. #2
    Reputation: derby's Avatar
    Join Date
    Jan 2004
    Without changing the big/big ring/cog combination, minimum chain length does not change for any rear derailleur.

    Compress the suspension to bottom (deflate shock), wrap chain around the big/big combo, add 2 links minimum to have a little slack for the derailleur when bottomed in that combo.

    Any shorter and the der is flexed and sucked into the spokes when bottoming when in the big/big combo gears, destroying both der and wheel (don't ask how I know!)

    Use a long enough cage so the chain in the small/small combo the cage clears itself.

    Shorter cages don't save significant weight. The minimum chain length is unaffected by cage length. Springs are much better now, so chain tension is not a problem with longer cages, but can be with too short of a cage.

    General rule with rare exception: 3 rings long cage, two rings medium cage, single ring short, although the huge cog range of XXI might require a medium cage.

  3. #3
    mtbr member
    Reputation: hardboiled's Avatar
    Join Date
    Jun 2006
    probably stating the obvious, but make sure both your frame and derailleur and compatible with the direct mount rear. I have a gen 1 frame which is not compatible. the early shadow plus der's aren't compatible either.

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