# Confused trying to work out if I need a GS or SS derailleur?



## fritzzz (Jul 10, 2010)

Hi,

I need to buy a new Ultegra 6700 derailleur but am confused if I need a short (SS) or medium cage (GS).

On the front I run 50 / 34.
On the rear I either run a 11 to 23 or a 12 to 25.

Shimano Technical Sevice Instructions say:-
_*SS*
Largest sprocket = 28
Total capacity = 33 teeth or less
Smallest sprocket = 11
Front chainwheel tooth difference = 16 teeth or less

*GS*
Largest sprocket = 28
Total capacity = 39 teeth or less
Smallest sprocket = 11
Front chainwheel tooth difference = 22 teeth or less

- The number of teeth on the smallest sprocket for SS-specification rear derailleurs is 15T.
- The number of teeth on the smallest sprocket for GS-specification rear derailleurs is 13T._

which seems to contradict the numbers in the table for largest and smallest

The SS will work with my front as that has a difference of 16 and they both suit the range of rears from 28 to 11 - is that all I need to consider?


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## sp3000 (Jul 10, 2007)

Yep, SS is the way to go.


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## wim (Feb 28, 2005)

> _- The number of teeth on the smallest sprocket for SS-specification rear derailleurs is 15T.
> - The number of teeth on the smallest sprocket for GS-specification rear derailleurs is 13T._


This refers to the _maximum_ number of teeth. The tech doc copy editor must have been out to lunch...


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## LongIslandTom (Apr 20, 2011)

You choose the SS or the GS depending on how much chain-slack take-up capacity you need.

For your particular gearing range (50/34 compact double and 12-25 cassette), an SS will work.

GS is for wider gearing ranges that will result in more chain slack when the drivetrain is crosschained small-small, like on triples or if you are running a very large cassette on a double.

I use an Ultegra 6700GS with an 11-32 cassette on a 50/34 compact double.


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## JCavilia (Sep 12, 2005)

Do you understand what's meant by "capacity"? It's the measure of how much slack the der can take up. It's the difference between the chainrings, added to the difference between largest and smallest cogs. In your case, 50 - 34 = 16, 25 - 12 = 13, 13 + 16 = 29 So you're well under the 33-tooth capacity of the short-cage. No problem.


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## DaveT (Feb 12, 2004)

Quick rule of thumb; if you're running a triple, you will need the GS 'long cage' derailleur. If you have a double crankset, then the SS 'short cage' derailluer is used.


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## fritzzz (Jul 10, 2010)

Thanks for the responses, it wasn't clear on the Shimano Technical Sevice Instructions what "capacity" meant and then the other notes re sprockets contradicted each other!

I'll won't have a triple on the front on this bike, could potentially end up with a 28 on the rear but not for a while so the SS is go. Appreciate everyone's help.


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## jeepseahawk (May 30, 2011)

If you ever go to 28 a ss will work just as well, just in case you are wondering.


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## fritzzz (Jul 10, 2010)

Brilliant- thanks!!!


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## CleavesF (Dec 31, 2007)

Just to add to the confusion... Long Cage works with EVERYTHING. Short doesn't.


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## Camilo (Jun 23, 2007)

> Just to add to the confusion... Long Cage works with EVERYTHING. Short doesn't.


Well, this is certainly adding to confusion because it's not true. 

A long cage road derailleur (use Shimano road groups just for example), generally does not have a larger capacity for rear sprocket size than the sort cage derailleur of the same derailleur, and that's probably around 28 teeth (give or take a couple, depending on the frame involved). I believe SRAM's long or medium cage RD's might have a capacity > 28, but it's still a general rule of thumb. 

It's really not confusing or difficult at all. As has been stated several times already: there are two simple specs that you need to look at for rear derailleurs - chain capacity and maximum rear sprocket. You simply look at two specs published w/ every derailleur and compare it to what you have or want to have on your bike.

But, again as has been pointed out already, if you do want to exceed the capacity of typical long cage road RD's with your bike (like using a big-sprocket MTB cassette), many/most mountain bike RD's are compatable with the same manufacturer's road shifters, they can handle the largest MTB cassettes made, and it's a very easy conversion. This is true for all Shimano 8 and 9 speed and Sram 10 speed, but I beleive there's issues with Shimano 10 speed (not sure about that having never done it.... but I've done the others).


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