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PostPosted: Tue Oct 01, 2013 11:58 am 
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Location: SW England
So I'm running a double with a 12-25 Cassette on a short Cage Centaur Derailleur.

I hate to have to even contemplate this concept, but, if I were to upsize my cassette ratio, what is the largest that would work with my setup? I'm just thinking about the possibility of some alpine ascents in the summer...

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PostPosted: Tue Oct 01, 2013 12:34 pm 
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You can do a 50/36 with a 13-26 cassette. I've done that with a short cage Record.

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Posted: Tue Oct 01, 2013 12:34 pm 


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PostPosted: Tue Oct 01, 2013 12:37 pm 
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Location: SW England
53/39 Double; not compact, sorry. Should have clarified.

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PostPosted: Tue Oct 01, 2013 12:50 pm 
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Pretty sure 28 is the maximum


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PostPosted: Tue Oct 01, 2013 12:54 pm 
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That sounds perfect. Can anyone confirm?

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PostPosted: Tue Oct 01, 2013 12:54 pm 
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I've run a 13/29 campag cassette on a campag short cage rear mech without a problem. This was despite campag recommending a long cage.


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PostPosted: Tue Oct 01, 2013 12:56 pm 
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There are 2 different issues when looking at this:

1. Will the upper jockey wheel clear the largest cog?

I just fitted a 12-29 (made up) cassette onto a friend's bike. It's close, but with correct chain length and adjustment of the "H" screw, it is running OK. The cage length is nothing to do with this clearance, all cage lengths have the same upper jockey wheel clearance. And Campy sells a 13-29 cassette.

2. Will the cage take up the chain between the Big-Big and small-small combo's?

The maximum takeup for a short cage RD is around 31T. So if running a 53/39 that's a 14T difference, leaving 17T. So, a 12-29 cassette is doable. Correct chain length is important.

The max of 31T can be exceeded as long as the chain is sized to be safe in the big-big. Some of the extreme crosses in the small ring will not be useable, but will not break anything.

My friend had a 50/34 compact up front. I sized the chain so that the big-big was safe. In running down the cassette in the small ring, that last useable cog was the 14T. RD ran out of takeup after that with saggy chain.
So 50/34 = 16T difference. 14 ->29 = 15T difference. Total 31T.

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Last edited by bikerjulio on Tue Oct 01, 2013 1:45 pm, edited 1 time in total.

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PostPosted: Tue Oct 01, 2013 1:03 pm 
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A racing buddy ran a 29 in an alpine social tour stage over Otira pass with no problem (5-6 years ago's record 10, I think.....may have been 11). He spun along nicely.....I grovelled.

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Posted: Tue Oct 01, 2013 1:03 pm 


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