rear mech choice

Discussion in 'Cycling Equipment' started by Graeme Beech, Jan 29, 2003.

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  1. Graeme Beech

    Graeme Beech Guest

    I am refurbishing a 1976 Raleigh Record Ace and need a new rear mech.

    The chainwheels are 52/42 and the new cassette I'm buying is 13/30 - hub spacing problems have been
    sorted out! Rear mech requirements are thus capacity 27, max sprocket 30.

    Shimano rear mechs have capabilities as follows SGS type: capacity 43, max sprocket 34 GS type:
    capacity 37, max sprocket 27 SS type: capacity 29, max sprocket 27

    Thus I appear to need the SGS type by virtue of max sprocket size; however the SGS is a large
    mountain bike mech which I would prefer to avoid.

    Will I be able to use a GS type despite the apparent max sprocket , bearing in mind its large
    capacity (37) compared with my requrements
    (27).

    Can anyone advise me?
     
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  2. In article <[email protected]>, Graeme Beech
    <[email protected]> wrote:
    >I am refurbishing a 1976 Raleigh Record Ace and need a new rear mech.
    >
    >The chainwheels are 52/42 and the new cassette I'm buying is 13/30 - hub spacing problems have been
    >sorted out! Rear mech requirements are thus capacity 27, max sprocket 30.
    >
    >Shimano rear mechs have capabilities as follows SGS type: capacity 43, max sprocket 34 GS type:
    >capacity 37, max sprocket 27 SS type: capacity 29, max sprocket 27
    >
    >Thus I appear to need the SGS type by virtue of max sprocket size; however the SGS is a large
    >mountain bike mech which I would prefer to avoid.

    It'll work fine, there's no strong reason to avoid it. Shimano MTB derailleurs are routinely used on
    road bikes, every day. The MTB design is also superior for use on very wide spaced clusters due to
    the angle of the parallelogram - your cluster has much bigger jumps than any that the SS/GS
    derailleurs were designed to run on (12-27 being the largest Shimano road cluster).

    >Will I be able to use a GS type despite the apparent max sprocket , bearing in mind its large
    >capacity (37) compared with my requrements
    >(27).

    Probably/usually yes.

    The GS type will often do 30t OK - since your front chainring difference is pretty small, you can
    usually eke a little extra cog clearance in back by running a slightly shorter chain (ie, there's
    a little extra chain tension when in low gear). Make sure it can still clear the big/big
    combination though.

    How well it works also depends on the shape of the derailleur tab on the frame.

    --Paul
     
  3. Graeme Beech wrote:
    > I am refurbishing a 1976 Raleigh Record Ace and need a new rear mech.
    >
    > The chainwheels are 52/42 and the new cassette I'm buying is 13/30 - hub spacing problems have
    > been sorted out! Rear mech requirements are thus capacity 27, max sprocket 30.
    >
    > Shimano rear mechs have capabilities as follows SGS type: capacity 43, max sprocket 34 GS type:
    > capacity 37, max sprocket 27 SS type: capacity 29, max sprocket 27
    >
    > Thus I appear to need the SGS type by virtue of max sprocket size; however the SGS is a large
    > mountain bike mech which I would prefer to avoid.
    >
    > Will I be able to use a GS type despite the apparent max sprocket , bearing in mind its large
    > capacity (37) compared with my requrements
    > (27).
    >
    > Can anyone advise me?

    The capacity ratings are highly conservative, and bear little relation to reality. See:
    http://sheldonbrown.com/gloss_ca-m.html#capacity for a detailed explanation.

    The setup you're describing will, in fact work with _any_ Shimano rear derailer, but I'd generally
    opt for the more versatile SGS type.

    Sheldon "Versatility" Brown +-----------------------------------------------------+
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    | knows his rider. Welcome to their roar! | Swift be their guidance, wheresoe'er it lead! | Though
    | the strain'd mast should quiver as a reed, | And the rent canvas fluttering strew the gale, |
    | Still must I on; for I am as a weed, | Flung from the rock, on Ocean's foam to sail | Where'er
    | the surge may sweep, | the tempest's breath prevail. | --Lord Byron Child Harold's Pilgrimage |
    +-----------------------------------------------------+ 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
     
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