abdon 

Please take a second and help me confirm this before I pull the trigger.

Time to upgrade the rear derailleur on my touring bike; I'm currently using a Tiagra rear derailer that was never meant to do 11-28t, nor used with a triple front (26/38/48). To that end I'm looking at the Ultegra 6700.

Here's the confusion: SS for double and GS for triple, right? Do both models come in short and medium cage or is ss short cage and gs medium cage?

Now, if GS comes in short and medium cage versions, what is the maximum cog size they are listed for? I see the SS listed as having a 28t cog capacity, but didn't find a capacity for the GS.

And is SL yet another variant?

Thanks in advance, mot appreciated.

davidad

On a tourer I would use a mountain rear DER.

bengreen79

If there is no problem with the gearing as is, I don't see any reason to switch to a MTB RD.

timg7

SS means short-cage, and has a 33-tooth capacity. You have a 22-tooth difference on the chainrings plus a 17-tooth difference on the cassette, so you'll need the GS (long-cage) variant which has a 39-tooth capacity.

The 105-series RD-5700-GS derailleur would also work.

The Ultegra-SL rear-derailleur is rated for a 37-tooth capacity and a maximum sprocket size of 27T (although it works ok for me with 28T).

abdon 

Thanks, I suspected as much but wasn't sure.

Why would a MTB be better? If the road bike derailleur has enough capacity, shouldn't that be it? 11-28 is as big as I care to go (used to have 11-32 & 48/38/28 and now I'm quite happy with 11-28 48/36/26).

While I have your attention, besides weight, what is the practical difference between the Ultegra and the 105? I'm running bar end shifters.

The other ulterior motive I have is my road bike. It has Dura Ace 7800 components, but I would like to regear it for the local terrain. The DA 7800 rear derailleur is stretched to the max on a 12-27 cassette, and I would like to see if the Ultegra derailleur would work with the 7800 shifters, on a 11-28 & 50/34 combo.

pmt

The DA rear will be fine with an 11-28 and 50-34. No problem.

Retro Grouch 

1. A mountainbike rear derailleur is designed to handle larger rear cogs. If you think that you might ever want to do loaded touring with a 32 or 34 rear cog, a MB derailleur would be an advantage.

2. How thin can you slice the baloney? Shimano has what - 5 or 6 road groups? They all do the job adequately. You've been riding with Tiagra so you know how that feels. My rule of thumb is that I can't feel any difference if I go up or down 1 group level but I can sense a slight difference in "crispness" if I move up or down 2 groups. The performance improvement is pretty uniform all up the line. The price difference as you move up the food chain, however, is exponential.

Gerry Hull

advantage of road over mtb derailleur in this application:

1. will maintain higher chain tension. Less likely to bounce off the front ring.
2. lighter by a couple of pennies, maybe.
3. no apprehension that people will think you are possibly are suffering from some sort of physical handicap for having an mtb der on your road bike.

Advantage of mtb der over road in this application:
1. the return springs tend to be lighter and make for easier shifting
2. use any cogset that pleases you. 11-36 if you want.
3. pivots likely to last longer since they're not being stretched to the max all the time. That translates into the derailleur shifting accurately for longer. I can't tell you how many guys Ive seen that cant get their chain onto the big cog of their 26tooth powerdomes because the derailleur is just pooped out.

Personally I wanted the best of both so I could use an 11-32 and dump the tiny front ring.
Got a deore, removed the cage. Next to the cage pivot is the little hole the spring fits into. Most ders have an additional hole (3/32) you can use that will substantially increase chain tension. If they dont, you get the nerve to drill one.

Some of these guys know a hell of a lot more about the different groups and their capacities than I do, but this is what I did and I love it. Before, I had a Tiagra like you so I know where your coming from.

In the past Ive used a Dura ace and Alivio and I cant tell much difference in shift quality. Hell I almost like the latter better because those giant jockey wheels run so quietly. But the geek factor there is too high even for me.
gh

abdon 

My original drive train was an 8 speed 48/38/28 with a 11-32. I changed it to a 9 speed 48/36/26 and a 11-28 and couldn't be happier. The -/26 28t combo is actually fairly close to -/28 32t. All I had at the time was a short cage tiagra which I put in a suicide setup; cross chaining is not an option and I mean, it is a physical impossibility

I still have quite a few years before I need a larger cog on the back. In the mean time, the short spacing really keeps me in the groove on incline and wind changes.

timg7

Any 105-5700 or Ultegra-6700 rear-derailleur should be fine with those shifters and that gearing combo. Even the short-cage "SS" version (just). A derailleur from the previous generation groupsets (5600 or 6600) will need to be the long-cage "GS" version.