Author Topic: Will a short cage 10 speed pre-2009 Chorus rear derailleur work okay with 12-27?  (Read 1739 times)

Will a short cage 10 speed pre-2009 Campagnolo Chorus rear derailleur work okay with a 10 speed 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've been offered the RD at a good price, but if I'm limited to 12-25 I'm going to struggle.

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 is a bit over spec. If this is going to be marginal, I do have a Veloce Medium cage RD to fall back on (which I assume I could even run a 12-30 Centaur cassette on), but since getting a bit fitter than 12-27 should be okay for most rides.
Old enough to know better, but young enough to do it anyway

my advice is to make sure you have enough chain length so that you can use the big-big combination and to accept that if you are daft enough to select the small-small combinations, the chain will run slack.  The exact capacity of the mech will vary with the installation; the mech will handle a 27T sprocket (on most gear hangers) but you will probably be marginal on total capacity.

cheers

my advice is to make sure you have enough chain length so that you can use the big-big combination and to accept that if you are daft enough to select the small-small combinations, the chain will run slack.  The exact capacity of the mech will vary with the installation; the mech will handle a 27T sprocket (on most gear hangers) but you will probably be marginal on total capacity.

Hmmm... that's sounding perhaps a bit too marginal to me for 27T, though the offer of a nice Chorus RD is tempting. Not sure I'm going to get fit enough to run a 12-25 all the time, though!

Maybe I should stick with the medium cage Veloce option, that would also (I *think*) allow me to run 12-30 if needed, which I might appreciate on the odd hilly sportive.
Old enough to know better, but young enough to do it anyway

I run Campagnolo short cage 10 rears on up to 29 rear sprockets with no issue, on 34/50 and 36/52 on different bikes.

I run Campagnolo short cage 10 rears on up to 29 rear sprockets with no issue, on 34/50 and 36/52 on different bikes.

Where year / model RD though? Think the later (post-2011?) ones have a slightly higher capacity, also a 13T cog would leave less slack than a 12T cog on small-small (not that you should do that).
Old enough to know better, but young enough to do it anyway

I run Campagnolo short cage 10 rears on up to 29 rear sprockets with no issue, on 34/50 and 36/52 on different bikes.

Where year / model RD though? Think the later (post-2011?) ones have a slightly higher capacity, also a 13T cog would leave less slack than a 12T cog on small-small (not that you should do that).

They’re all sorts of years, from alloy cage to carbon cage. I also run 11 and 12 smallest on occasions. OK, 36x11 does leave a little slack, but who would use that? The most important thing is to get the small screw that alters the tension on the cage right.

BTW I asked Velotech Cycling Ltd. about this, who are the main UK Campagnolo Technical Centre and got this lengthy answer:

"You are correct, the combination that you want to run does exceed the designed capacity of the derailleur with a frame and gear 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).

Slack 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 disastrous 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 irrelevant - these things are not governed by production, they are governed by a combination of frame geometry, exerted 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. "

Old enough to know better, but young enough to do it anyway

Mine do. I recently got 12-29 and 13-28 and didnt have to anything to the  rear screw even tho' I had bought a derailleur extension just in case. the 12-29 works flawlessly on the same chain as the 12-25/13-26 that I switch between but I never run big-big

Mine do. I recently got 12-29 and 13-28 and didnt have to anything to the  rear screw even tho' I had bought a derailleur extension just in case. the 12-29 works flawlessly on the same chain as the 12-25/13-26 that I switch between but I never run big-big

Is that on a 50/34 compact, though? Also 12-29 and 13-28 are not standard Campagnolo 10-speed cassettes - are yours Miche ones?
Old enough to know better, but young enough to do it anyway