I'm running Ultegra 6800 with
- a 52-34 chainring up front (not a typo: I replaced the 36 with a 34), and
- a 6800 GS (medium cage) derailleur at the back, and
- a 12-29 rear cassette.
It works well.
My question is this: could I drop in an HG800 11-34 cassette?
I am aware that this would exceed the max total capacity (41t instead of 37t) and also the maximum sprocket (34t instead of 32t), as per Shimano's documentation here: http://bike.shimano.com/content/sac-bike/en/home/components11/road/ultegra1/rd-6800-gs.html But I'm already exceeding the maximum front difference (18t from 52 to 34, instead of the claimed maximum of 16t) --- with no ill effects.
Shimano is notoriously conservative. Does anybody know if it would actually work?
In summary: would a set-up with 52-34 up front, 11-34 at the back, work with a medium cage Ultegra 6800 derailleur?