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  1. #1
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    chain stay angle

    How important are the chain stay angle numbers I get off of my old front derailleur?

    I want to replace a crapped out fd that specifies 66 to 69 degree.

    Here is the one I want to get. http://www.jensonusa.com/store/produ...erailleur.aspx

    The specs of the new one match the old {top pull, clamp size** but I can't find any info from jenson on chain stay angle numbers on the new.

  2. #2
    rebmeM roineS JanMM's Avatar
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    Never heard of chain stay angle numbers related to FD selection/compatibility.
    Could those numbers be important for an FD attached to a brazed-on fitting?
    RANS V3 (steel), RANS V-Rex, RANS Screamer

  3. #3
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    I've never heard of "chainstay angle" being a consideration in fd selection either. I have heard of seattube angle as a parameter so I assume it's the angle between the seat tube and chainstay they are referring to.

    I expect unless your frame is way out of the ordinary, there should be no problems.

  4. #4
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    No my old one is clamp on with those numbers stamped on it.

    Look at this tech doc and you'll see Shimano has chain stay angle specs for fd's


    http://bike.shimano.com/publish/cont...patability.pdf

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    Well, If Shimano publishes the specs, you can be certain that frame manufacturers pay attention.

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    Well I found through velospec that the fd I'm looking at does have 66-69 degree whatever. So I guess it's workable. Still, I wonder why it is a spec.


    http://velospec.com/components/shimano/fdm580

  7. #7
    rebmeM roineS JanMM's Avatar
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    Quote Originally Posted by scylla View Post
    Well I found through velospec that the fd I'm looking at does have 66-69 degree whatever. So I guess it's workable. Still, I wonder why it is a spec.


    http://velospec.com/components/shimano/fdm580
    Maybe it's just for the benefit of framebuilders, as HR suggests.
    RANS V3 (steel), RANS V-Rex, RANS Screamer

  8. #8
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    That must be the angle between the seat tube and chainstay. In the linked table there is only 3 degr little difference between models. I am sure you will only have a problem if you are fitting an extreme range of chainring sizes, and run them cross-chained.

  9. #9
    Senior Member Road Fan's Avatar
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    I think its the orientation of the chain guide. The chain guide has a certain vertical dimension, from the bolt at teh botom of the cage up to the edge at the front where it has to clear the large chainwheel. On a frame with a more laid back seat tube the same derailleur can span across a wider range of front chainwheel sizes.

    As the chainstay angle becomes more acute with respect horizontal, the chain moves up in the chain guide, allowing a smaller front sprocket to be used.

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