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PostPosted: Tue Oct 01, 2013 11:58 am 
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Joined: Fri Apr 12, 2013 1:19 pm
Posts: 739
Location: South West 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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Scott CR1 - 7.1kg - dead
BMC SLR02 - 7.6kg - dead

Kinesis Aithein - ~8kg


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PostPosted: Tue Oct 01, 2013 12:34 pm 
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Joined: Fri Jan 27, 2006 1:38 pm
Posts: 662
Location: Greater Pittsburgh
You can do a 50/36 with a 13-26 cassette. I've done that with a short cage Record.

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PostPosted: Tue Oct 01, 2013 12:37 pm 
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Joined: Fri Apr 12, 2013 1:19 pm
Posts: 739
Location: South West England
53/39 Double; not compact, sorry. Should have clarified.

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Scott CR1 - 7.1kg - dead
BMC SLR02 - 7.6kg - dead

Kinesis Aithein - ~8kg


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PostPosted: Tue Oct 01, 2013 12:50 pm 
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Joined: Mon May 14, 2012 11:49 pm
Posts: 32
Pretty sure 28 is the maximum


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PostPosted: Tue Oct 01, 2013 12:54 pm 
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Joined: Fri Apr 12, 2013 1:19 pm
Posts: 739
Location: South West England
That sounds perfect. Can anyone confirm?

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Scott CR1 - 7.1kg - dead
BMC SLR02 - 7.6kg - dead

Kinesis Aithein - ~8kg


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PostPosted: Tue Oct 01, 2013 12:54 pm 
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Joined: Mon Jan 12, 2004 12:32 pm
Posts: 3689
Location: HULLGARIA UK
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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Joined: Fri Dec 11, 2009 10:38 pm
Posts: 1513
Location: Welland, Ontario
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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There's sometimes a buggy.
How many drivers does a buggy have?

One.

So let's just say I'm drivin' this buggy...
and if you fix your attitude you can ride along with me.

http://www.youtube.com/watch?v=GekiIMh4ZkM


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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Joined: Sun Jun 12, 2005 10:56 am
Posts: 2672
Location: New Zealand
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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Updated: Racing again! Thought this was unlikely! Eventually, I may even have a decent race!
Edit: 2015: darn near won the best South Island series (got second in age
-group)..woo hoo Racy Theremery is back!!


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