# Will a short cage 10 speed Chorus rear derailleur work okay with 12-27 and 50/34?



## Oxford_Guy (Oct 25, 2018)

Will a short cage 10 speed pre-2010 Campagnolo Chorus rear derailleur work okay with a Centaur 12-27 cassette and compact 50/34 chain set without any drama? I try not to cross chain small-small or large-large, but don't want a disaster if that happens.

I think Campagnolo say a max cog size of 26T, but that was before the 12-27 cassette was available. Chain wrap would be 31 teeth, which I think may be slightly over spec.


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## gfk_velo (Jun 17, 2013)

Oxford_Guy said:


> Will a short cage 10 speed pre-2010 Campagnolo Chorus rear derailleur work okay with a Centaur 12-27 cassette and compact 50/34 chain set without any drama? I try not to cross chain small-small or large-large, but don't want a disaster if that happens.
> 
> I think Campagnolo say a max cog size of 26T, but that was before the 12-27 cassette was available. Chain wrap would be 31 teeth, which I think may be slightly over spec.


You are correct, the combination that you want to run does exceed the designed capacity of the derailleur with a frame and gera hanger that are compliant with the Campagnolo spec.

You would need to run a chain 1 link longer than optimal to be safe in "big to big" bit this would mean inadequate tension in small-to-small, with the result that you would have a slack idler run on probably the smallest two sprockets (depends on frame geo how bad this is).

Slacl chain on small to small is not in itself a disaster BUT - it can lead to quite a bit of lateral whip in the chain and an increased risk of the chain being caught on the back of the big ring and giving a chain-suck type effect which can be a bit disasterous for your paintwork (and in an extreme case can lead to a chain so thoroughly jammed that you end up bending a chainring and / or having to drop the crankset off to free the chain.

The fact that Campagnolo launched 12-27 after the max sprocket and capacity information was released is largely irrelevent - these things are not governed by production, they are governed by a combination of frame geometry, exected chain tension, front and rear derailleur design / geometry.

At one time, Campagnolo made a compact crankset with a 48 outer in 10s, for instance, which could be used with a 12-27 cassette if a compromise was made in the setting of the "H" screw, or on bikes with a rear derailleur hanger at the upper end of the hanger length specification. That could actually be worked around by changing the H screw drive ratchet for a longer one from the 11s component range ... it all depends what compromises a user is willing to make on function and how much modification a mechanic is competent to make and in new material, whether warranty is an issue that matters to the end user.


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## Oxford_Guy (Oct 25, 2018)

Okay, shame, that sounds like "not really recommended", due to the issues you mentioned. I can run a Medium cage Veloce RD, but the Chorus would've been nicer. Looks like you can still get 10 speed Record RDs, but expensive and too much carbon really for the build I have in mind 

Can you get an alloy medium cage conversion kit for the Chorus RD?


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## Oxford_Guy (Oct 25, 2018)

BTW with a *medium* cage 10-speed Veloce (most recent generation - RD11-VLXM) or Record (older - RD4-REXM) derailleur would it actually even be possible to run a 12-30 Centaur cassette with a compact chain set? Don't think I need that for regular use, but could be useful for trips to the mountains (or Yorkshire...).


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## Bee-an-key (May 5, 2007)

Since it is only one tooth beyond the limit you should be good with the right chain length. I may be wrong but you also have to research the capability of some of the lower end rear derailleurs with the higher end shifters and capacity. There have been generations where the tech won't let you run them all together. I am sure someone will correct me if I am wrong.


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## Oxford_Guy (Oct 25, 2018)

Bee-an-key said:


> Since it is only one tooth beyond the limit you should be good with the right chain length. I may be wrong but you also have to research the capability of some of the lower end rear derailleurs with the higher end shifters and capacity. There have been generations where the tech won't let you run them all together. I am sure someone will correct me if I am wrong.


Shifters will be 2006-era Veloce or Record (so Ultrashift, effectively) 10 speed.


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