# Ultegra 6800 Long Cage/Short Cage RD



## Sask

My first post – and so much to learn!I just ordered a complete road bike that comes with the new Ultegra 6800 group, and includes the new 11-32 cassette and the long cage (GS) Shimano rear derailleur. I don’t want/need an 11-32 (no component switching allowed).

If I swap the 11-32 for an 11-28 or 12-25 do I: a) have to switch to the short cage RD for either or both cassettes; and b) will the chain have to be shortened for either or both cassettes?I’m hoping I can use either the 11-28 or 12-25 on the short cage and keep the same chain length for both, or either cassette on the existing long cage -- I hope I’m not stuck in between where the 11-28 and the 12-25 can’t operate properly on the same size RD.

I realize there could be a whole other discussion about why I would even consider wanting to have both of these cassette ranges instead of one or the other – let’s not go there!Your comments/advice would be appreciated.

Not sure if it matters but forgot to say that it's a 50-34 crank.


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## brianmcg

A. No B. Maybe.


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## PJ352

For whatever reason, a lot of people think RD's have to change with taller/ lower rear gearing. That's not the case. In fact, the specs for max/ min cogs are generally the same for SS/ GS RD's. 

The only reason to change to a GS RD is because the front chainring tooth difference and/ or total tooth capacity exceeds the specs - see below for an example:

http://techdocs.shimano.com/media/t...SI-5X90B-003-00-ENG_v1_m56577569830702204.PDF

BTW, you're current configuration is 37 total teeth, thus the GS RD.


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## Kerry Irons

Sask said:


> My first post – and so much to learn!I just ordered a complete road bike that comes with the new Ultegra 6800 group, and includes the new 11-32 cassette and the long cage (GS) Shimano rear derailleur. I don’t want/need an 11-32 (no component switching allowed).
> 
> If I swap the 11-32 for an 11-28 or 12-25 do I: a) have to switch to the short cage RD for either or both cassettes; and b) will the chain have to be shortened for either or both cassettes?I’m hoping I can use either the 11-28 or 12-25 on the short cage and keep the same chain length for both, or either cassette on the existing long cage -- I hope I’m not stuck in between where the 11-28 and the 12-25 can’t operate properly on the same size RD.
> 
> I realize there could be a whole other discussion about why I would even consider wanting to have both of these cassette ranges instead of one or the other – let’s not go there!Your comments/advice would be appreciated.
> 
> Not sure if it matters but forgot to say that it's a 50-34 crank.


No and no. 

If the chain length is correct for that rear derailleur, then it will not need to be shortened when you go to a smaller cassette size. If the RD can wrap all the chain needed for the "as sold" configuration then it will have zero problem doing the same for the cassette size you propose.


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## Sask

Thanks for the replies.

To Kerry: It's good to know that I can stick with the GS RD and use either the 11-28 or 12-25 cassette.

To PJ352: I read through the Shimano technical document. I must admit that I don't understand what is meant by "Total capacity"; and please explain how the 37 total teeth is calculated (I really should look this up on my own!).


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## PJ352

Sask said:


> To PJ352: I read through the Shimano technical document. I must admit that I don't understand what is meant by "Total capacity"; and please explain how the 37 total teeth is calculated (I really should look this up on my own!).


Your 11-32 cassette represents a span (or difference) of 21T. Your 50/34 chainrings represent a difference of 16. Add the two and you have a total tooth count of 37, two lower than the max capacity (39) of a GS RD.

Not to confuse you further, but (as an example) if you had an SS RD and your compact crankset, either of your new cassette options would work because total teeth would be 33 (with an 11-28) or 30 (with an 11-25).


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## Sask

That was a very clear explanation. Thanks for walking me through that -- much appreciated!


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## MaynardK

PJ352 said:


> Your 11-32 cassette represents a span (or difference) of 21T. Your 50/34 chainrings represent a difference of 16. Add the two and you have a total tooth count of 37, two lower than the max capacity (39) of a GS RD.
> 
> Not to confuse you further, but (as an example) if you had an SS RD and your compact crankset, either of your new cassette options would work because total teeth would be 33 (with an 11-28) or 30 (with an 11-25).


Sorry to jump in here late on this, but I'm thinking of building a 1x11 Ultegra 6800 setup with the 50 x 11-32. I never - really, never - use the small chainring. Not even on the steeper hills I climb. It'll be simple: one less chainring, one less derailleur, less cable and less housing. I digress.

Given the calculation you mentioned, PJ352, I think I'd be good with the SS RD seeing how the chainring will never change from the 50T. However, the maximum cog spec'd is 28T. Are they saying that's the "maximum capacity" meaning it will work (my capacity being 21) or the largest cog size (32T)? Do you think the SS will have enough extension to work the 32T cog size?

Thanks for any help you can give!


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## cxwrench

No...that won't work. There are 2 things to be aware of:
Maximum 'capacity' (how much chain the derailleur will 'wrap',
and
Maximum cog size.

They are 2 completely different things. The GS derailleur geometry has been changed to work w/ a 32t cog. This is a new development, in the very recent past both SS and GS derailleurs always had the same maximum cog spec.
'Wrap' is the difference between the small and large cogs ADDED to the difference between the large and small chainrings (if you are in fact running more than 1 chainring, which you are not).


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## MaynardK

That's much clearer. Thanks for the quick hit back.

Parts are ordered and I'll post pics after the build.

Thank you!


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## cxwrench

Posts like these should also be made in the 'components/wrenching' section for obvious reasons.


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## MikeWMass

MaynardK said:


> Sorry to jump in here late on this, but I'm thinking of building a 1x11 Ultegra 6800 setup with the 50 x 11-32. I never - really, never - use the small chainring. Not even on the steeper hills I climb.
> Thanks for any help you can give!


Just out of curiosity, why not save some money and just use a tighter cassette? Or go with a standard crank. The weight penalty will not be great, you will have at least tighter gearing and possibly also a higher top end, and you will not have either an unused left shifter or mismatched brake levers (please notice I did not use "brifter"). IMO, front derailleurs are not much hassle, the cables don't seem to snap off inside the shifters like Shimano rear cables do.


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## cxwrench

MikeWMass said:


> Just out of curiosity, why not save some money and just use a tighter cassette? Or go with a standard crank. The weight penalty will not be great, you will have at least tighter gearing and possibly also a higher top end, and you will not have either an unused left shifter or mismatched brake levers *(please notice I did not use "brifter")*. IMO, front derailleurs are not much hassle, the cables don't seem to snap off inside the shifters like Shimano rear cables do.


Rep'd :thumbsup:


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## MaynardK

cxwrench said:


> Rep'd :thumbsup:


Thanks *cxwrench* and *MikeWMass*. I think I'm able to make sense of most of your input. I'm still a rookie, though, so I don't think I understand some.

*q_*
Will disconnecting the FD cable from the left shifter leave the shift-lever portion flopping around without tension or will the shifter be fine (spring-loaded somehow)?

I'm going with the new Ultegra 6800 11sp because I got a great deal and am offloading the 105 setup that came on the bike. I also wanted Ultegra vs. an XT 10sp (11-32 or 11-36) because of the quality of shifting.

Bottom line, I'm just going to dig having a much simpler setup. A 1x11 with a 50x11-32 will give me the entire range I need. A la Ben Berden's cross bike setup.


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## cxwrench

It won't flop around.


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## venture

cxwrench said:


> No...that won't work. There are 2 things to be aware of:
> Maximum 'capacity' (how much chain the derailleur will 'wrap',
> and
> Maximum cog size.
> 
> They are 2 completely different things. The GS derailleur geometry has been changed to work w/ a 32t cog. This is a new development, in the very recent past both SS and GS derailleurs always had the same maximum cog spec.
> 'Wrap' is the difference between the small and large cogs ADDED to the difference between the large and small chainrings (if you are in fact running more than 1 chainring, which you are not).


So, you are saying is not just the cage that is different? I figures the body of the SS and GS were the same, and it was the cage that was different - the length of the cage and the placement of the top pulley.

My expectation is, if you replace the cage on an SS RD with a GS cage, you will end up with a GS RD. Is this true, or are there more differences?


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## MMsRepBike

venture said:


> So, you are saying is not just the cage that is different? I figures the body of the SS and GS were the same, and it was the cage that was different - the length of the cage and the placement of the top pulley.
> 
> My expectation is, if you replace the cage on an SS RD with a GS cage, you will end up with a GS RD. Is this true, or are there more differences?


The body of the GS derailleur is different on 6800/6870. It's built for larger cassettes, it replaces the need for a triple up front.


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## PJ352

venture said:


> So, you are saying is not just the cage that is different? I figures the body of the SS and GS were the same, and it was the cage that was different - the length of the cage and the placement of the top pulley.
> 
> My expectation is, if you replace the cage on an SS RD with a GS cage, you will end up with a GS RD. Is this true, or are there more differences?


There are more differences, two being the shape and length of the RD body.



MMsRepBike said:


> The body of the GS derailleur is different on 6800/6870. It's built for larger cassettes, it replaces the need for a triple up front.


The max/ min sprocket capacities of the RD-6800-GS and RD-6870-GS are the same. What's changed is the 6870's _lowered_ max front ring difference (16T versus 22T) and max tooth capacity (37T versus 41T)

It's not so much that the 6870 'replaces' the need for a triple. More accurately, assuming a span of more than 16T, it cannot support it. A step back, IMHO.

product

Product


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