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All: I am running a 10sp Campy Centaur group with compact (50x34) chainrings. The 50t ring is a Mirage and the 34t ring is Chorus/Centaur. These are both replacement rings. Since the new rings were installed (several thousand miles ago), when shifting from the 50t to the 34t the chain will sometimes fall between the rings and slip. Usually, I have to shift back to the big ring and then down again; occasionally I have to dismount and seat the chain by hand. My LBS doesn't seem to know what the cause of this is. I do not remember having this problem with the original Centaur rings, but that may be coincidental, and I'm reluctant to buy new rings unless I'm pretty sure that is the problem. Derailleur adjustment seems fine.

Has anyone heard of this or had similar issues? Any advice or experiences? Thanks a lot.

Cheers,
Andy
 

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'brifter' is f'ing stupid
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I've seen that kind of thing happen from time to time, but without seeing your particular bike in the stand i have no idea where to start. I'd bring it by another shop and see if they can find the cause. Most like it's the position of the derailleur or the adjustment. Could also be some compatibility issue w/ the chainrings.
 

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Lost in Space...
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Any idea what year the front derailleur is? I know that some of the older ones require the FD to be at a slightly off angle but that was fixed in 2008 or 2009... I don't imagine that would cause the problem your are having but it's worth throwing out there.
 

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Matnlely Dregaend
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The spacing is different on the stamped vs the machined Campy rings, and they aren't compatible from Centaur down to Chorus and up. Centaur is a little tricky because some Centaur 10 speed cranks used stamped chain rings and some used machined ones. The best way to check is to put the old rings back on and measure the spacing and compare that to what you have now. For some 10 speed cranks the bolt hole on the crankarm is also offset, resulting in a bent chain ring if you install one that's not compatible.
 

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As cxwrench has said, difficult to diagnose over the net. But I would try a small adjustment of the front derailleur first. Sometimes, it may well be adjusted to Campy specs (chain on small ring - largest cog and 0.5 mm clearance between inner cage plate and chain), but that setting could be just shy of producing reliable shifts for a variety of possible reasons. Try increasing that clearance just a bit and see what happens (you may have to disconnect the cable). When you think about it, the perfect adjustment is not a specified clearance, but "a perfect shift every time without the chain ever going into the frame."

If you have some time on your hands and are curious, adjust the derailleur (repair stand) where the chain will in fact come off the small ring and start going into the frame. That way, you have an idea of how much clearance is too much.
 

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Similar experiences have been posted before e.g.

http://forums.roadbikereview.com/campagnolo/10-speed-ut-downshift-problem-284470.html

I can get this to happen once in a while if I shift down to the 34 when I'm in the 7th or 8th rear cog (never tried 9 & 10) which is not very often. I though it was maybe me or my bike until I read the above thread last year. Now my brother is getting the same thing on his new Centaur equipped bike and again only if he is on the smaller rear cogs and even then it doesn't happen every time
 

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No doubt this problem can and does occur with Campy UT cranks. But chain-skatiing on the front is really a very common issue that happens across all brands and models of components.
I'm sure it is but as my experience is with Campy only, that's all I can comment on. (BTW, my brother's bike is PT not UT.)

Because of this, the solution almost always is a generic fix, not something related to "Campy only."
Maybe or maybe not. I have years of experience in setting up and using Campy and only experienced this fairly recently. I'm confident my set-up is correct (and I have tried moving things around a bit). The problem is that it is intermittent and hence difficult to tie down. My brother gets the LBS to do his set-up and although we have different bikes (Wilier and Bianchi) he also experiences the skating chain on occasions.

I look forward to the generic, universal fix to this, although it must be said it isn't one of these things that keep me awake at night!
 
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