Originally Posted by
xfimpg
Thanks Al, makes perfect sense.
I also noticed the following when I'm in the 50 ring (using a 12/27 cassette):
Gearing:
50 ring with 27 = no rub
50 ring with 24 = no rub
50 ring with 21 = no rub
50 ring with 19 = rubbing = applying trim creates more rubbing
50 ring with 17 = rubbing = applying trim removes rubbing
50 ring with 15 = no rub
50 ring with 14 = no rub
50 ring with 13 = no rub
50 ring with 12 = no rub
I would expect rubbing on one of the middle cogs, and then apply the trim the quiet it out.
In this case I can hear it over 2 cogs; i've played with the cable tension and all it does is move the rubbing down to the 15 gear and still spread over 2 gears. Really strange.
FYI - ultegra derailleur front and back, fsa 50/34, ultegra 12/27, basic Shimano chain (not Ultegra); all of these are brand new.
Would you happen to know what the problem could be?
First I would look for any cable housing problems that could cause excess friction.
How old are the cables and cable housings, if they are dirty or corroded that might explain your problem.
Dirt in the short housing just before the rear derailleur is often a problem.
Check the cable routing at the fixing bolt on the rear derailleur. The cable needs to run through a small groove. If the cable is on the wrong side of the fixing bolt it will cause strange shifting problems.
Be sure the lockring is tight enough. A loose lockring can cause the cogs to float around enough to cause problems. It's not normal to have any chain rub with the chain in the middle part of the cassette.
Al