Originally Posted by
Iride01
Trim should only be needed when you are in a cross chaining situation between the front and rear. Sometimes you'll hear the chain rubbing on the FD cage when in the last cog on the rear or even the one cog prior. It simply lets the FD move over a little bit to allow for the sharp angle that is being made in the chain line from rear to front.
If you add trim to help with the chain noise, then you need to remember to remove it if you shift the rear back in the other direction and don't shift the front to the other ring.
You really need to pay attention to how they tell you to set up the FD and adjust it in the instructions. Sometimes with Shimano FD's, the trim setting won't work well if things aren't adjusted correctly enough.
Thank you Iride01.
I do having the chain robbing FD cage problem. When I use the large chainring and shift to the last 2 large cogs, the robbing starts. When I use the small chainring and the smallest cog, it also robs but I can do up-shifting to the trim to handle it. I can not find a method how to get the front derailluer down-shifting from the high position to the trim. When I press the down-shift lever, the front derailluer put the chain to the low chainring. It does not keep the chain on the large chainring and move a little to the trim to resolve the robbing.