Classic & Vintage - can an 8 speed DA rd handle a 28T cog?

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fatallightning
03-18-09, 06:46 PM
i know shimano docs say no, but there is often wiggle room. empirical evidence? chain wrap issues? going on a 52/42 chorus double.

-holiday76
03-18-09, 07:16 PM
velobase says 26 is that max:

http://velobase.com/ViewSingleComponent.aspx?ID=B9BE2FB8-66F2-42BA-985D-A2FE24E8C20D&Enum=108&AbsPos=36

That said, it's worth a try.
RobbieTunes
03-18-09, 07:44 PM
Mine isn't supposed to, haven't pushed it.
I have an 8-sp 600 RD doing just that. Chain length is critical. And I mean you have to have it right on.

tuz
03-18-09, 07:59 PM
From my experience with other Shimano dérailleurs (105 and XT), I'd say yes. You will probably have to tighten the B-screw and shorten the chain, as RobbieTunes said. Since the front is a 52-42 the chain wrap should remain ok.

Give it a try and let us know!
fatallightning
03-18-09, 08:52 PM
how do i calculate chain length? i believe i have something like an 11-21 mounted now.
tuz
03-19-09, 06:52 AM
how do i calculate chain length? i believe i have something like an 11-21 mounted now.

Your chain is too short: it won't wrap the 52x28. I'd add 3 or 4 links. Ideally the small-small should not be too loose and the big-big not too tight.

or check here (http://sheldonbrown.com/derailer-adjustment.html#chain).