I recently set up a new gravel bike with all new components, including a 2x11 GRX DI2 drivetrain. 31/48 and 11-36t. It has ridden under 600 miles and only seen rain once. It is accident free and has never been dropped.
When in the large chainring, and shifting up into a smaller sprocket quickly, starting around the 7th or 8th sprocket, the chain bounces from side to side. While pedaling, the outer face of the chain links occasionally hit, and get stuck on, the outer plate of the front derailleur cage.
Last week, when pedaling at high speed and force, it even broke off the derailleur braze-on clamp.
The chain length is according to the instructions (4 links longer on big big combo). I also tried a chain with 4 links less, but it did not help.
The b-screw is set according to spec - with a ~5mm gap between the pulley and the large sprocket. I also tried increasing the chain tension (gap between pulley and largest sprocket was close to 20mm), but it did not help.
The front derailleur is set up correctly (aligned with outer chainring, and about 1 mm gap between outer plate and chain when in highest gear, and 3mm above the large chain ring)
The rear derailleur clutch is engaged and the torque is around 4Nm. I already cleaned and lubed it, but it did not fix the issue. I also tried increasing the tension to 5.5Nm, but it did not help. Turning the clutch off does not help.
I serviced the rear hub. It did not help.
I installed a brand new chain and cassette, but it did not fix it. For clarity, I had a 11-34 Shimano cassette with a 1.85mm spacer originally when this issue first occurred. I am now running a 11-36 Sram PG-1170 without spacer.
We tried out a different GRX crankset to rule out the likelihood of the chainring being bent or worn. It did not help
I had two bike shops look at it, but they could not find a solution (but validated that there is an issue).
The bike shifted fine for the first month. Or at least, it was fine enough not to bang the front derailleur cage. I do not know what has changed since then.
My next steps are
- upsize the pulley wheels
- replace the rear derailleur
- go back to riding my old bike :cry:
Do you have any ideas on what else might fix this issue? I really want to jump back on this dream bike but don't know how to fix it. Thank you!
—— Update: I tried out a friend’s mechanical GRX810 RD, and it worked like a Charme. We compared the geometry and noticed that mine doesn’t spring back nearly as far to support the smaller sprockets. Mine looks like the one in the first picture in its “neutral” state:
I am contemplating replacing my cage with one for a GRX810 or similar.