I am getting a strange grinding/vibration through the pedals on certain gears. I notice it when in the 2nd and 3rd largest cogs in the back and the big ring up front. Originally I thought it was cross-chaining, but when I go into the biggest cog on the back I don't seem to hear it. It also only seems to happen when under heavy load (e.g. climbing out of saddle).

I am riding an 11-spd Ultegra Di2. Chain/cassette have less than 2k miles on them and the bike is shifting well.

I can't for the life of me figure out what is going on. Any insights would be much appreciated!

Have you tried readjusting the front derailleur to make sure it is lined up corrrctly?

That's what it sounds like. :-)

Chordal action?

2.2.1 Chordal Action

It is supposed to increase with smaller sprockets but riding fixed gear I find that some front/rear combinations just seem worse regardless of sprocket size.


-Tim-