My current drivetrain setup is 50x34 and 11x34. The chainring is a Rotor Q-ring, cassette is Shimano Ultegra, and the rear D is Ultegra RD8050GS; Shifting is on shimano Ultegra Di2.
I am thinking about changing my chainring to 53x39, Rotor Q-ring as well, but keeping my 11x34 cassette. Is it possible to have this setup with my rear D without the chain slapping around too much on in the easier gears? With my current setup (50x34 11x34) the chain becomes slack if I’m in 34x15; granted I shouldn’t be in such a low gear in the first place, but it happens if I downshift from the big ring.
Yes, 53/39 X 11-34 should be fine. That falls within the specs on the RD.
This sounds like a potential setup issue, specifically chain length. I personally use the Small-Small chain length setup which prevents the slack issue you describe.
Thanks @mcneese.chad ! I wonder if part of the issue is the Q ring, as the chainring rotates I can see the rear d flexing as the gear inches changes throughout the pedal revolution.
EDIT: That is to say, I wonder if the shop added slack to the chain because they were concerned it’d be too tight over the top of a higher gear, e.g. 50x27, and damage the rear D?
The Q-Ring may require a bit more attention since it is effectively be longer in some parts of the rotation. I don’t happen to know the delta there and if it exceeds the RD range really. But the RD spec is a 16t max delta at the front big to small.
50 - 34 = 16 that matches the limit
53 - 39 = 14 which is under the limit, which is potentially better from the perspective of handling the “extra” within the Q-ring, but that is a guess.
Sure could be, but I wouldn’t know without running it through the range and checking RD angles and chain tension. Probably a good question for the tech that set it up.
