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  1. #1
    Spinone Italiano Fat Boy Biker's Avatar
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    Meaning of cage length in rear derailluer

    What is the meaning in cage lenght for the rear derailluer (short versus long, maybe even a medium). It is my understanding that a long cage for the front derailluer is for a 3 chain rings, and a shorter cage would be for 2 (over simplified I'm sure). But how does length come in to play in the rear?

    Thanks,

    Steve
    -confused, and trying to build a bike
    Pedal fast, feel the wind in your face, be grateful that life is good.

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  2. #2
    Senior Member sydney's Avatar
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    Chain wrap capacity.Longer wraps more chain. Generally regarded as needed for a triple and sometimes used with a compact double and wide range cassette. Formula for the wrap spec you need: big chainring teeth-smallest chainring teeth + large cog teeth- small cog teeth = required wrap capacity. The 30 granny on the typicall 30/42/52 triple adds an addtitional 12 teeth of required wrap, relative to a 42/52 double.

  3. #3
    Senior Member Retro Grouch's Avatar
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    The "cage" is tha arm that extends downward from the derailleur. It's function is to take up the chain slack as you shift into smaller sprocket combinations. While saying that a long cage is for 3 front chainrings and a short cage is for 2 chainrings is somewhat oversimplifying, it's close enough for most applications.

  4. #4
    Spinone Italiano Fat Boy Biker's Avatar
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    Quote Originally Posted by sydney
    Chain wrap capacity.Longer wraps more chain. Generally regarded as needed for a triple and sometimes used with a compact double and wide range cassette. Formula for the wrap spec you need: big chainring teeth-smallest chainring teeth + large cog teeth- small cog teeth = required wrap capacity. The 30 granny on the typicall 30/42/52 triple adds an addtitional 12 teeth of required wrap, relative to a 42/52 double.
    Great explanation. Thanks Sydney.

    Steve
    -a little less confused.
    Pedal fast, feel the wind in your face, be grateful that life is good.

    -2000 Gary Fisher (red and yellow)
    -2006 Scanttante CFR (black beauty carbon)
    -the 2002 Bianchi Giro (red) found a new home after 3000+ miles

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