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  1. #1
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    Stumpjumper comp - rear derailleur / chain length question

    This may be a noob question, but I'm not sure what to do here. My LBS says it's normal and I find that hard to believe.

    Anyway, I've found that when I'm in any of the 2-3 smallest cassettes in the rear and the smallest ring in the front, my chain rubs on itself as it moves through the derailleur. I know this is cross chaining and shouldn't be done anyway, but this doesn't happen to friends with similar setups and I find it hard to believe that it's normal. I've already screwed the b (tension) screw all the way in on the rear derailleur. I thought my only other option would be to shorten the chain......but I'm not so sure I have enough chain to do that.

    See the pics below.

    IMGP0654 [1024x768].JPG
    IMGP0653 [1024x768].JPG
    These pics are with the chain in the 2 largest rings. To me, it doesn't appear there's much room to shorten the chain. Is there?

    IMGP0655 [1024x768].JPG
    This pic is smallest ring in the front and 3rd to smallest ring in the back. The chain is ALMOST touching, but not quite.

    IMGP0658 [1024x768].JPG
    IMGP0657 [1024x768].JPG
    These pics are smallest ring in the front and 2nd to smallest ring in the back. The chain is now touching.

    IMGP0659 [1024x768].JPG
    IMGP0660 [1024x768].JPG
    These pics are smallest ring in the front and smallest ring in the back. It's obviously pretty crowded back there in this gear.

    Again, I know this is severe cross chaining, but I still feel that this must be abnormal. Is my LBS full of it? Or am I just a noob? (or a little of both?)

    Any thoughts on what I should do to remedy? Thanks everyone.
    Attached Images Attached Images

  2. #2
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    There are 3 standard cage lengths on derailleurs; short, mid, and long. The X9 you have on the Stumpie Comp is a mid-cage derailleur, instead of a long cage derailleur. The long cage (with a longer chain) gives you a bit more clearance in the smallest cogs front and rear. The trade-off is slower shifting. A mid-cage derailleur will shift up and down both smoother and quicker than a long cage, but your chainring-gear combo's get limited. You can take out a link to improve the clearance, but you run the risk of doing damage if you ever shift to the large chainring-large cog combo. If the chain is too short, you can break derailleurs, chainring teeth, or the chain. The B-tension adjustment won't help you much in this case, I would ajust it back to the correct setting to prevent the derailleur pulleys from clashing with the cassette cogs.

    There are other pro's and con's to the different size cages like chain whip, and increased risk of grabbing bad things like rocks and branches. You can dig the info up on the web.

    There are a couple calculators on the web which will figure the correct chain length based on derailleur cage, cassette gears and chainrings. Shimano and SRAM have different cage lengths for comparably named cage sizes.

    I personally like the quicker shifting of the mid-cage, and readily pop up to a bigger chainring when I need to pull a bigger gear.

  3. #3
    I think I need to Upgrade
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    That is normal and like that for a reason. Why? So you don't break your chain or rip off your rear der. if you go Big Big. Have someone sit on the bike and then look at how the chain and der. cage are, you will most likely notice that they are no longer making contact. The gear combination that you have it in should never be used anyway so the way the chain in sitting while in that gear combination is completely irrevelant.

    Short version.... Everything is fine, if you shorten the chain you you will probably break something, now quit thinking about it and go ride your bike but first LUBE THAT CHAIN!!! it looks dry.

  4. #4
    I think I need to Upgrade
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    [QUOTE=rsvrjimbo02]
    There are a couple calculators on the web which will figure the correct chain length based on derailleur cage, cassette gears and chainrings. Shimano and SRAM have different cage lengths for comparably named cage sizes.
    QUOTE]


    Unless these chain length calclators allow you to specify exactly what frame you have (each model full suspension frame has different chain growth) you will end up breaking parts. PLEASE DON'T USE THESE CALCULATORS ON A FULL SUSPENSION BIKE.

  5. #5
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    Thanks to you both. Great information and exactly what I needed to hear.

    Two follow-up items:

    1) You're absolutely right that the chain needs some lube . Just got back from a dusty ride here in CO.

    2) I assume, to prevent cross chaining, that I should only be in the 3 or 4 largest rings in the rear while in smallest ring in the front, middle 3 or 4 rings in the rear while in middle ring in the front, and smallest 3 or 4 rings in the rear while in the largest ring in the front? If that's the case, that's definitely going to take some practice to remember when I'm on the trail and just looking for a suitable gear.

    Thanks again guys - really appreciate the advice.

  6. #6
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    You're not really supposed to fully cross chain (big-big or small-small) on a MTB or any triple either, so if you shift to the middle ring before you go to the small cog, you'll be much better off.
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  7. #7
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    The real objective when running front/rear combos is to keep the chainline reasonable, in addition to pulling a gear you need. Anytime you are runnning a gear combo that cross chains (small cogs-small ring or big cogs - big ring), you are putting stress on the chain and gear teeth. This causes premature wear of both, and risks breaking something. Cross chaining to the extreme should be avoided.

    When running on the middle chainring, you should be able to hit all 9 cassette rings without any major issues. If your chainline is true, then you should be okay. The chainline on my Stumpie is spot on for the middle chainring - 5th gear. Yours most likely is also.

  8. #8
    I Am Specialized
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    I'm glad I am not the only one who asked the same question.
    2009 Specialized Stumpjumper FSR Comp | 2009 Specialized Roubaix Comp | 2008 Specialized Langster New York

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