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PostPosted: Thu Feb 13, 2014 12:33 am 
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Joined: Tue Nov 11, 2003 9:47 pm
Posts: 2196
Location: Santa Cruz, California, USA
I've always avoided making the chain too short to handle the big/big combo. Because even though I don't use big/big and usually keep pretty good track of what gear I am in, a couple times I have had serious oxygen debt, high altitude or extreme fatigue cause my brain to malfunction so much that I have shifted into the big/big combo. If the chain's too short the ride is going to end there. If there's not enough wrap I'd rather it be slack on the small/small. A slack chain won't instantly destroy the bike or derailleur the way a too short chain will.


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Posted: Thu Feb 13, 2014 12:33 am 


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PostPosted: Thu Feb 13, 2014 8:54 am 
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Joined: Tue Apr 12, 2011 8:08 am
Posts: 2292
Location: Pedal Square
eric wrote:
[...] shifted into the big/big combo. If the chain's too short the ride is going to end there.

Not my experience. Once put a 34t cassette on a long cage RD-6700 to see it would clear (which it did), with the chain length set for 27t max. One could just not shift from the second to the biggest cog, with good resistance feedback on the lever. Only cautiously tried on the stand, though. If you tried to shift with brute force, maybe things would go wrong. But you could clearly feel something was not right, even without looking. (Also not sure of what would happen with an electronic RD).

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PostPosted: Thu Feb 13, 2014 9:32 pm 
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Joined: Tue Nov 11, 2003 9:47 pm
Posts: 2196
Location: Santa Cruz, California, USA
Cautiously on the stand, yea no problem. On a ride when your brain is foggy, well I would not expect a happy outcome.

Even on the stand I have run into trouble with a too short chain. The derailleur cage caught on a cog and stuck the whole thing. I got it apart without much damage but it took some fiddling.


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PostPosted: Thu Feb 13, 2014 10:23 pm 
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Joined: Tue Apr 12, 2011 8:08 am
Posts: 2292
Location: Pedal Square
Yes well driving the mech into the cluster is something else. If the RD doesn't clear the top cog, don't even think about riding, because it will not work with the small ring either.

But generally agreed, better safe than sorry. In my case I was using a big cassette just for a hillclimb. All small-ring business, no danger of cross-chaining.

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PostPosted: Fri Feb 21, 2014 1:35 am 
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in the industry

Joined: Sun Jun 15, 2008 4:57 am
Posts: 456
Location: Newport Beach, CA
FIJIGabe wrote:
We all know that Shimano did not make a mid/long cage rear derailleur for the DA9000 level. However, I recently acquired an Ultegra 6800 GS rear derailleur, and I don't see why the long cage wouldn't work on my DA derailleur, other than the weight penalty.

With that in mind, does anyone know anywhere that makes, or would be willing to make, a longer RD cage? I contacted Fibre-Lyte, and they have no plans to make such a beast, and none of my searches have provided me with an answer.

Thanks.


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PostPosted: Mon Apr 07, 2014 3:30 am 
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Posts: 70
Where can one buy one of these cages from berner or K edge? I seem em on google images but not in any stores.

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PostPosted: Mon Apr 07, 2014 5:48 am 
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Joined: Sat Jul 20, 2013 6:11 pm
Posts: 1127
my LBS says they have done a number of ultra mid cages to 9070 Di2 RD with no issues... I was just going to go 6870 di2 RD mid... but they actually brought it up... my build is waiting on 9000 cranks with stages... so I am still ~3-4 weeks from my build.


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PostPosted: Sat Apr 01, 2017 10:34 pm 
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Joined: Thu Mar 12, 2015 12:44 pm
Posts: 13
Location: Stockholm, Sweden
A few years late to the party here, but still felt like I should add my recent experience to the thread. For me swapping in a 6800-GS cage onto my Di2 9070-SS rear derailleur did not work well at all.

My problem was that the upper pulley on the 6800-GS medium cage is a few millimeters closer to the cassette than on the original 9070-SS short cage. This was enough of a difference that the pulleys and chain wouldn't clear the largest cog on the cassette, even with an 11-28T cassette that would normally work fine with the original short cage.

Of course this will also be very much affected by the geometry of your rear derailleur hanger. My bike is a Canyon Ultimate CF SLX 2013 with the original rear derailleur hanger #25. A longer B tension screw doesn't help much either, as the ledge on the derailleur hanger is much too small. As I turn in the longer screw eventually it will be nearly perpendicular to the ledge and then simply slip of it…

Looking at Canyon's website they also have a slightly longer hanger #28 which could potentially resolve my issues. Might try ordering one of those.


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