Re: Misc TA Crankset questions

Discussion in 'Cycling Equipment' started by A Muzi, Oct 15, 2004.

  1. A Muzi

    A Muzi Guest

    Retro Bob wrote:

    > Easy question:
    > Are TA Cyclotouriste chainwheels the same bolt pattern
    > as Stronglight 49 ? Will the TA triple bolts work on the 49 ?
    >
    >
    > Harder question for advanced students:
    > On Sheldon's site, it says that you want to do a half step plus
    > granny" setup with this TA crank. It infers (if I'm reading it right)
    > that it will be difficult to shift the small to medium wheel if the
    > medium is not close in size to the large (outer) chainwheel.
    >
    > http://sheldonbrown.com/harris/french-cranks.html#cyclotouriste
    >
    > I'm having trouble grasping this, or I'm just reading it wrong.
    > Why would the medium to large size chainwheel relationship
    > impact the small to medium shift ? I would think that you'd want
    > the medium closer to the middle of the range for the smoothest
    > shifting from the small to medium.
    >
    > I have no reason to doubt Sheldon... just trying to understand
    > the issue.


    With unramped and unpinned rings, you'll often need to shift
    past the middle slightly to make that shift and the chain
    can't easily climb past the outer when the difference is large.

    You can put a _set_ of #49D rings on a TA arm but not just
    the middle or inner ring.
    --
    Andrew Muzi
    www.yellowjersey.org
    Open every day since 1 April, 1971
     
    Tags:


  2. Tim McNamara

    Tim McNamara Guest

    Retro Bob <[email protected]> writes:

    > What's considered a "large" difference? 7 teeth? 10 teeth?
    >
    > What did they do in the 70's when we had 32/42/52 setups with double
    > type derailleurs ? Did they just tolerate shift problems ?


    That's only a 10 tooth difference. Most road setups available at the
    bike shop use a 14 tooth difference (39 to 53) routinely. You could
    use a 53-39-24 combination probably with success, although shifting
    would be less than ideal.

    > What does a "triple" derailleur have that's different to help with
    > the larger difference ?


    Look at the shape of the inner plate of the derailleur cage in some
    catalogs. The inner plate reaches lower. Look at the outer plate-
    the curvature of the edge of the plate on a road deraileur is shaped
    to match the larger chainring; on a MTB derailleur the curve is shaped
    for the smaller 44-46-48 tooth big rings commonly used. So you can't
    jus randomly throw a MTB front deraillur on a road bike. However,
    there are some "road triple" front derailleurs from Shimano and
    Campagnolo.
     
  3. A Muzi

    A Muzi Guest

    Retro Bob wrote:
    > What did they do in the 70's when we had 32/42/52 setups with
    > double type derailleurs ? Did they just tolerate shift problems ?
    >
    > What does a "triple" derailleur have that's different to help
    > with the larger difference ?


    Wide-range triples were, at one time, lousy shifting
    generally and hence less common.

    There were at one time both alpine and half-step front
    changers. The inner alpine cage will hit the middle ring of
    a half step. The half-step front changer is not so deep on
    the inside cage.

    TA outers are supplied drilled to accept a middle/inner of
    43t ( Criterium) or of 36t ( Randonneur - rare) or of 26t (
    Cyclotouriste- most common). There are several adapters,
    too. The rings join with six bolts.

    Stronglight's 49D uses a 5-bolt inner ring with a minimum of
    38t, same as a Stronglight #63 or a Stronglight #93. The
    outer ring to crank 5-bolt interface is the same for both,
    and also Williams, Cyclo, Sugino Dynamic, maybe others.
    --
    Andrew Muzi
    www.yellowjersey.org
    Open every day since 1 April, 1971
     
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