kc4sox

I just bought a Domane 5.2 with 6800 Ultegra 11-28 11 speed cassette. On my Madone I was running a 10 speed 12-30 and I'm missing that 30 cog. I want to change out my 11-28 for the 12-32. Can I do this without having to buy a medium cage Derailleur ? Bike is currently sporting the short cage.

Any other options ?

Xherion

It will work. It's not ideal and not recommended by Shimano, but plenty of people have done it. I'd be a bit more hesitant if you have a 53 large chain ring though.

Rear derailleurs are cheap though, only around 50 bucks for a 6800 medium cage.

Paul Barnard

I just tried running a 30 with a DA short cage and it wouldn't work. Compact crank.

NYMXer

From what I know, even with a medium derailleur, you might still have issues. I would say the least you would need is a medium. I have a medium and want to swap out the 28 for a 30, and that is a tight fit for a medium, or so I was told. I am not an experienced bike mechanic but a good parts changer. I do not know what works with what just yet, but I know which people to ask for advice and that's what they told me. I trust them.

twodownzero

Your chain is just too short. Mine works fine with a 105 medium cage, 12-30 rear. I would not try it with a short. Front ring is 48/38/26. Max front difference 22, total tooth capability 40 teeth. AKA, right on the edge of spec.

Xherion

You need to find a new mechanic or friends who know what they're talking about. The GS derailleur is specced by Shimano for up to a 32, which is still conservative. I can even speak from experience, I have an 11-32 on a 6800 derailleur and it easily fits. Hell, with a road link and a longer B screw, you can even fit a 40t on it with a medium cage.

rms13

Right:

RD-6800-GS

Probably need a longer chain though

Bike Gremlin

If you are careful enough not to ever use small/small combo, you can get away with it. Measure the chain moving it around big rings front and back (without going through RD), add one link and you're good to go. If moving to small-small, it will start making noise, reminding you to shift up to the big ring.

The other option that causes less chain drop chance and gives a bit quicker shifting is to cut the chain a bit shorter, so that it can't exceed the RDs chain wrap capacity, but in case of shifting to big-big, you risk tearing the RD out and ruining it.


Big 32 ring at the rear is not a problem. The limit is total tooth difference. If a short cage is used with say 39-50 crank and a 12-32 cassette, it should work fine, have enough chain wrap. Wrote a bit more here:

measuring chain length and what to do when exceeding chain wrap capacity:
Chain length sizing for bicycles with derailleurs

rear derailleurs explained - chain wrap, cog size limits etc:
Rear derailleur