Originally Posted by
FBinNY
The description doesn't make sense to me.
Do you mean that the chain somehow drops to the inside of the inner ring when trying to shift it outward? That's hard to accept, though it is fairly common when shifting from outer to inner. OTOH do you mean its dropping between the two chainrings?
Getting a clear description of what, how and when, will help others offer possible solutions.
Yes, it drops to inside of inner/small when shifting from small to large. See response from other person below. That is what is happening.
Originally Posted by
choddo
Is the small chainring on backwards?
This is possible. I was having a hard time figuring out which is out and which is in. I think I have it correct but now that you mention it, I can't be sure. There is an indentation. What is the right way? Can you explain the mechanics involved with the problem if installed backwards?
Originally Posted by
tFUnK
The reason it drops on the inside is because the chain is trying to jump from small to large but having trouble catching on, and if the pedal stroke isn't smooth, or if the road buzz is causing the chain to jump around, it'll fall back down towards the small ring due to the chain tension, but it slips off the small ring for some reason. I've had this happen on mechanical FDs of the cable tension isn't high enough or the FD high limit is not set far enough, such that the throw of the front shifter isn't quite enough to help the chain make the jump onto the large ring. No experience with Di2 (eg, can you adjust the throw) but it could be just a case of needing to set the high limit correctly.
Yes, this is what is happening.
Thanks everyone.