Problem statement - when I back-pedal in big-big the chain ships down to the small ring. I noticed this when switching chainsets (52-36 to a 50-34) and fitting a new BB. It may have been a thing that could've happened before but never did.
I've swapped mech hanger, rear mech, other 50-34 chainset, rear wheel, back to the original BB - the issue persists. Sram red22 GXP on a modern steel frame, chain and cassette are new.
Does anyone have any ideas? Is it looking like the frame is the problem?
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