Di2 Ultegra Rear Mech Rd-6870. Will the short cage SS work with single chainring 11-32 cassette?

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Ed209
Posts: 34
Joined: Wed Jul 08, 2015 1:55 pm

by Ed209

My race bike is a single chainring with 11-32 cassette.

I'm planning on upgrading to Di2. My question is whether the short cage RD-6870 will fit over the 32t cassette? I don't need the chainslack tensioning ability of the medium cage (since I'm only running single chainring) but will the top pulley of the SS RD-6870 fit over the 32t cog?

Does the medium cage Rd-6870 also have a longer body, or is it just the cage that's longer?

Ritxis
Posts: 1119
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by Ritxis

Rd-6870 with 11-32, chainring 42, alfine di2 levers
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by Weenie


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Ed209
Posts: 34
Joined: Wed Jul 08, 2015 1:55 pm

by Ed209

Ah perfect Ritxis! I recognise your bike from another time you helped me with 1x11 di2.

Finding a SS on ebay will be a lot easier than finding a GS. Thanks.

Ed209
Posts: 34
Joined: Wed Jul 08, 2015 1:55 pm

by Ed209

Ritxis wrote:Rd-6870 with 11-32, chainring 42, alfine di2 levers


Just want to check, that is a SS RD-6870, and not a GS?

Ritxis
Posts: 1119
Joined: Fri Jun 01, 2012 3:00 pm
Location: San Sebastian

by Ritxis

Ed209 wrote:
Ritxis wrote:Rd-6870 with 11-32, chainring 42, alfine di2 levers


Just want to check, that is a SS RD-6870, and not a GS?



Yes, Rd-6870 short cage (SS)

eric
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Location: Santa Cruz, California, USA
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by eric

The max cog spec is 28t. With Shimano being conservative, 30t is almost allways doable but 32t often is not. It depends on your frames derailleur hanger.

Ritxis
Posts: 1119
Joined: Fri Jun 01, 2012 3:00 pm
Location: San Sebastian

by Ritxis

eric wrote:The max cog spec is 28t. With Shimano being conservative, 30t is almost allways doable but 32t often is not. It depends on your frames derailleur hanger.


In Scott Cr1 2017 no problem rd SS with 32, in Felt Z1 with DA Di2 no problem with cog Miche 30, no problem with DA mechanical rear derailleur, fellows of foromtb used without problems Rd-9070 with 32, You must be careful not to use large chainring with large cogs (28 or 32) I recommend to add at least a link more to the chain

eric
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by eric

I would strongly suggest making the chain long enough to go over both the big ring and largest cog. If it's short and you shift into that combination by mistake while putting out power it'll rip the derailleur right off the frame.

Ed209
Posts: 34
Joined: Wed Jul 08, 2015 1:55 pm

by Ed209

This is all a non-issue anyway if the only difference between SS and GS is the cage length and not the actual body.

metabo
Posts: 14
Joined: Sat Oct 15, 2016 4:02 am

by metabo

Ed209 wrote:This is all a non-issue anyway if the only difference between SS and GS is the cage length and not the actual body.

Not sure it's the case with RD-6800/RD-6870. I think the GS version has a deeper slant angle, so that you can keep the proper clearance between the big cogs and the guide pulley more easily, which otherwise you have to make it by adjusting the B tension bolt.

I can also confirm SRAM's longer cage derailleurs (called WiFLi) have the bodys slightly differing from the shorter ones.

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allenpg
Posts: 136
Joined: Tue May 20, 2008 5:34 am

by allenpg

I've only ever pushed my SS to a 28t. I have GS on my CX bike that works fine with a 36t. Now, I'm tempted to try my SS with a 32t...:)

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