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PostPosted: Mon Apr 24, 2017 12:49 am 
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Joined: Sat May 12, 2012 8:32 am
Posts: 740
Location: Adelaide, Australia
I've recently bought a bike that came with a medium cage RD, but I have no need for a medium cage and want to swap to a short cage. Since it's di2 I'd like to avoid a new rear mech if possible. I was wondering if I could just swap the cage from a mechanical derailleur. I've seen a few threads suggesting that going short -> medium isn't the best idea (better to just buy a new RD) but is the converse also true (medium -> short)?

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Posted: Mon Apr 24, 2017 12:49 am 


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PostPosted: Mon Apr 24, 2017 1:28 am 
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Joined: Tue Oct 23, 2012 10:52 pm
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Location: PHL
Send me a PM if you want to trade for my lightly used short cage 6870 rd

Sent from my SM-G925T using Tapatalk

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PostPosted: Mon Apr 24, 2017 10:19 pm 
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Joined: Wed Jun 06, 2012 11:43 pm
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Why the reluctance to use the medium cage you have? There is no performance gain by going to the short cage. Is it just the extra few grams? (Understandable given the forum and all that)

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PostPosted: Mon Apr 24, 2017 10:33 pm 
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Joined: Wed Dec 30, 2015 12:41 am
Posts: 269
In your case i don't think it save you anything (other than few grams) going down to short cage.

There is one case experienced by me that short cage serve better than mid cage mech.
It's Sram Red 22 mechanical on a pretty long drop out of a Chinese carbon fiber frameset.
Mid cage version of the groupset (Sram Red RD, Wifli) not only longer in cage but also longer on B-knuckle. When combined with long drop out, i need to turn B-tension screw all the way out to get pully reasonably close to the cassette. And that make rd tilt in a pretty bad angle for cable entrance and it's quite hard to change the wheel with pulley going very far forward of the cassette.
On short cage and short B-knuckle RD, it's only half way out B-tension screw to use 11-28 with closer upper pulley to the cassette and better cable entrance for RD (thanks to my longer than usual RD hanger). Perfect set-up for me would be short B-knuckle with long pulley cage (as i use 52/34+11-28 in the front, it work on short cage right now but too close to the limit than i'd like).

but in your case that you are doing the opposite, i'm not sure if it'll give you anything.


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PostPosted: Mon Apr 24, 2017 10:44 pm 
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Joined: Sat Oct 31, 2009 7:35 pm
Posts: 160
To answer the original question- you can go from short to medium or vice versa just by changing the cage. If you look at the exploded views you can see that those are the only parts different between the versions. That said, I have a medium cage derailleur and have had no performance problems with a whole variety of cassette sizes.


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Posted: Mon Apr 24, 2017 10:44 pm 


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PostPosted: Tue Apr 25, 2017 12:07 am 
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Joined: Sat May 12, 2012 8:32 am
Posts: 740
Location: Adelaide, Australia
Thanks for the replies. I was just worried that the angles, or some internal thing that I'm not aware of would be different. But it appears as though I can buy a mechanical 6800 rear mech and swap the cage + b-tension screw and I should be ok.

@Pokerface07: Not trying to save weight with the short cage, but I just find wheel changes easier with it. For some reason the long cage is a bit harder to 'wrap' and 'unwrap' around the cassette - perhaps I'm just used to the short cage and haven't learnt the proper technique for long yet.

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I write the weightweenies blog, hope you like it :)

My SwiftCarbon Ultravox

My Velocite Selene

Disclosure: I'm sponsored by Velocite, but I do give my honest opinion about them (I'm endorsed to race their bikes, not say nice things about them)


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