Backpedaling on highest gear (11t) causes chain to pop up/out off at the front top part of the smallest cog. The bike and all components are very new and stock. This is a 1-by Shimano GRX Drivetrain. Any way to fix this or optimize the drivetrain?

chain popping

Video: https://i.sstatic.net/jedJw.jpg

Rear Derailleur: Shimano GRX RX812 GS
Cassette: Shimano SLX M7000 11-42 11s
Crank: Shimano GRX RX600 40T
Chain: Shimano HG701 11-speed

I noticed some wear on top of cage, could it be related? cage wear

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    Bicycles with derailleurs are not designed to be pedaled backwards. Instead of the chain being pulled tight at the top with the derailleur sucking up slack at the bottom, the chain gets dumped off the top of the cranks with the mere hope that the tension from the derailleur can provide enough force to keep the chain in tension despite all friction from the freewheel, the chain bending around the cogs and derailleur jockey wheels, and the jockey wheel bearings. If there's too much friction, the chain goes slack and can go anywhere. If you don't like what happens when you do it, stop doing it. Commented Mar 25, 2022 at 20:09

1 Answer 1


I think this might simply be unavoidable with such a chain line/angle (though it’s hard to tell from the video). If the chain is too long it might be exacerbating the problem. Make the chain shorter if it’s possible.

Those scratches on the rear derailleur look deep. Did you backpedal with force, causing the chain to tangle up everything? Was there an oopsie where you dropped the chain into the rear wheel spokes (limit screw too far out) and kept pedaling?

If the B-screw is not screwed in far enough the derailleur can hit the big sprockets, which could cause similar damage.

There is way too much lube on that chain. Wipe it down after lubing. Excess lube on the outside only attracts dirt.

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