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  1. #1
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    Rear der cage size

    I am in the process of finishing up my winter build but am having problems with one final decision. My new ride is a niner air9 with a sram xx crank with 26-39 chainrings. Ay cassette is a 12-36. According to sram's website, I can run a med cage lengh rear der. I have heard of others running a large. which one works better? Anyone run both and have better luck with one or the other. I am thinking i am gonna be running either a xo or x9 for the rear der. Any help would be great.

  2. #2
    Huckin' trails
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    Quote Originally Posted by mtb4146 View Post
    I am in the process of finishing up my winter build but am having problems with one final decision. My new ride is a niner air9 with a sram xx crank with 26-39 chainrings. Ay cassette is a 12-36. According to sram's website, I can run a med cage lengh rear der. I have heard of others running a large. which one works better? Anyone run both and have better luck with one or the other. I am thinking i am gonna be running either a xo or x9 for the rear der. Any help would be great.
    Rule of thumb is the shorter the cage, the crispier and faster shifting will be. Usually derailleurs have a max tooth count capacity, for rd it's calculated by total of bigger chainring minus smaller chainring tooth count, plus the total for largest rear cog minus smallest cog tooth count.

    In you case it will be : (39-26) + (36-12) = 37 teeth difference. So your rd needs to have at least a 37 teeth capacity. The rest is yours.
    Quote Originally Posted by NicoleB28 View Post
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  3. #3
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    thanks for the help.......great info you got there

  4. #4
    Never Forget 9-11
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    I'm running a 24/38 with a 12/36 with no problems on a medium cage.
    It's such a fine line between idiocy and genius.

  5. #5
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    I was running 26-39T with 12-36 and a medium x0 derailleur. Small-small combo (26/12) didn't have enough tension for the chain, but all other gears worked fine. Really you shouldn't be in small-small anyways, so go medium.
    RideSAMBA.com Mountain Biking in South Alabama.

  6. #6
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    Quote Originally Posted by paulrb02 View Post
    I was running 26-39T with 12-36 and a medium x0 derailleur. Small-small combo (26/12) didn't have enough tension for the chain, but all other gears worked fine. Really you shouldn't be in small-small anyways, so go medium.
    that is not so, one of the hypes about 2x10 gearing is that all combos are available and will work.

  7. #7
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    Until recently, I ran XO 39/26 cranks with an 11-36 cassette using XX medium cage rear derailleur. This setup works well and there was no need for a long cage rear derailleur.

    In the Drivetrain forum here on MTBR there is a multi page thread entitled "when to use a long cage vs. short cage rear derailleur." The thread is stickied here: When to use a Long Cage vs Short Cage Derailleur?

    I have not any of the thread but it might be helpful in to the OP.

  8. #8
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    Quote Originally Posted by therollex View Post
    that is not so, one of the hypes about 2x10 gearing is that all combos are available and will work.
    That hype was with the original XX derailleur, which is now the long version.

    but really, the medium is fine, and you'll have snappier shifters and more clearance, if you happen to edge off the trail a bit.
    RideSAMBA.com Mountain Biking in South Alabama.

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