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Old 01-01-10, 03:21 PM   #1
scylla
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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.
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Old 01-01-10, 03:28 PM   #2
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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?
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Old 01-01-10, 03:36 PM   #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.
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Old 01-01-10, 03:41 PM   #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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Old 01-01-10, 03:53 PM   #5
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Well, If Shimano publishes the specs, you can be certain that frame manufacturers pay attention.
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Old 01-01-10, 04:01 PM   #6
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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
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Old 01-01-10, 05:42 PM   #7
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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.
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Old 01-01-10, 08:08 PM   #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.
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Old 01-02-10, 01:50 AM   #9
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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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