put on new chain the other day (old cassette, has approx 4000km on it)
& took off cassette and cleaned it, also put on new derailleur hanger cos the other one got bent and wasn't really fixed properly by the shop..
easy peasy so far, indexed the gears which takes literally 20 seconds cos it's di2. drivetrain is now PERFECT. lubed up and ready to go
however.... when i am in big cog/big cog (50-32), the chain will immediately come off if i pedal or rotate backwards for more than about half a turn. Chain comes off inwardly towards the frame, every time.
google says either:
a)ignore and don't pedal backwards you idiot (ok fine but y'know sometimes it just happens, or you wheel it backwards to park or whatever)
b) something to do with the B screw but i done a lot of b screwing in and out & it don't make a difference.
(i know google also says don't use that gear combo but sometimes i do ok? Not very often but i don't want to have to remember to avoid it at all times because I will forget).