conventional wisdom on MTB derailleurs?

Discussion in 'Cycling Equipment' started by Ant, Aug 10, 2003.

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  1. Ant

    Ant Guest

    A friend was putting a new chain on his mountain bike, and was wondering aloud about how long to
    make it. I read, a long long time ago, Sheldon's big-big-and-one, and have been using it without a
    single exception for the last 80 chains i've installed. no exaggeratin'. and as i always test gears
    after installing the chain, which puts me through both of the crossed combinations, id come to
    believe that the method was infallible.

    so, i told my friend to step aside and let me show him my 'infallible' method. as it turns out, it
    left the chain so slack in the small-small that there was a sizeable droop in the chain even after
    the der had folded itself all the way back.

    shocked, i had to come to grips with an explanation to protect my ego ;)

    does he need a longer derailleur cage, or is this standard fare for mtbs? his explanation: i never
    use the big ring with the bigger rings in the back. But that wouldnt do it for me on my bike.

    thoughts?

    anthony
     
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  2. ant wrote:
    > A friend was putting a new chain on his mountain bike, and was wondering aloud about how long to
    > make it. I read, a long long time ago, Sheldon's big-big-and-one,

    Although I recomend it, I can't take credit for it.

    > and have been using it without a single exception for the last 80 chains i've installed. no
    > exaggeratin'. and as i always test gears after installing the chain, which puts me through both of
    > the crossed combinations, id come to believe that the method was infallible.
    >
    > so, i told my friend to step aside and let me show him my 'infallible' method. as it turns out, it
    > left the chain so slack in the small-small that there was a sizeable droop in the chain even after
    > the der had folded itself all the way back.
    >
    > shocked, i had to come to grips with an explanation to protect my ego ;)
    >
    > does he need a longer derailleur cage, or is this standard fare for mtbs? his explanation: i never
    > use the big ring with the bigger rings in the back. But that wouldnt do it for me on my bike.

    This "droop" doesn't do any actual harm, however riding in the small-small combination with a modern
    MTB drivetrain is EXTREMELY abusive. The itty-bitty granny ring can put an enormous amount of pull
    on the chain, and the itty-bitty 11 tooth rear sprocket is only sharing the load amoung 5 or at best
    6 teeth/chain rollers.

    Even leaving the bad chain angle out of consideration, using this combination cause greatly
    increased chain and sprocket wear. The small-small combination should _never_ be used on a triple
    crank setup, especially a modern "compact" type.

    Even the second smallest rear cog should be avoided when you're using the granny chainring.

    See also: http://sheldonbrown.com/gloss_ca-m.html#capacity

    Sheldon "Not A Problem If You Use Your Gears Properly" Brown
    +--------------------------------------------+
    | Life is what happens to you, | while you're busy making other plans. | --John Lennon |
    +--------------------------------------------+ Harris Cyclery, West Newton, Massachusetts Phone
    617-244-9772 FAX 617-244-1041 http://harriscyclery.com Hard-to-find parts shipped Worldwide
    http://captainbike.com http://sheldonbrown.com
     
  3. David Kunz

    David Kunz Guest

    ant wrote:

    > A friend was putting a new chain on his mountain bike, and was wondering aloud about how long to
    > make it. I read, a long long time ago, Sheldon's big-big-and-one, and have been using it without a
    > single exception for the last 80 chains i've installed. no exaggeratin'. and as i always test
    > gears after installing the chain, which puts me through both of the crossed combinations, id come
    > to believe that the method was infallible.
    >
    > so, i told my friend to step aside and let me show him my 'infallible' method. as it turns out, it
    > left the chain so slack in the small-small that there was a sizeable droop in the chain even after
    > the der had folded itself all the way back.
    >
    > shocked, i had to come to grips with an explanation to protect my ego ;)
    >
    > does he need a longer derailleur cage, or is this standard fare for mtbs? his explanation: i never
    > use the big ring with the bigger rings in the back. But that wouldnt do it for me on my bike.

    I have the same problem with my Cannondale Jekyll -- and I'm using a long cage XTR DR. But if I make
    the chain shorter, I'll probably break or bend something if I accidentally hit the big-big
    combination (night riding). Also remember that the small-small combination is to be avoided because
    of the angle the chain makes with the gears.

    David
     
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