Bicycle Mechanics - 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/product/FD604A03-Shimano+Lx+Fd-M580+Front+Derailleur.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.

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?

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.

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/content/global_cycle/en/us/index/tech_support/tech_tips.download.-Par50rparsys-0016-downloadFile.html/10%29%20Drivetrain%20Compatability.pdf

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

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

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.

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.

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.