Ultegra Di2: Medium cage to short cage

Discuss light weight issues concerning road bikes & parts.
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istigatrice
Posts: 790
Joined: Sat May 12, 2012 8:32 am
Location: Australia

by istigatrice

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

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)

prebsy
Posts: 762
Joined: Tue Oct 23, 2012 10:52 pm
Location: PHL

by prebsy

Send me a PM if you want to trade for my lightly used short cage 6870 rd

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Pokerface07
Posts: 205
Joined: Wed Jun 06, 2012 11:43 pm

by Pokerface07

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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Hexsense
Posts: 374
Joined: Wed Dec 30, 2015 12:41 am

by Hexsense

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.

djwalker
Posts: 165
Joined: Sat Oct 31, 2009 7:35 pm

by djwalker

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.

istigatrice
Posts: 790
Joined: Sat May 12, 2012 8:32 am
Location: Australia

by istigatrice

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

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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