The frame on my rain bike has the RD cable guide brazed to the top of the BB shell. When the infrequent chain drop occurs, the chain sometimes gets jammed between the cable guide and the granny ring which can be a real pain to free up...
especially in the rain. It's not simply just a matter of lifting it back up onto the chainring.
The FD
is adjusted properly but still isn't perfect 100% of the time.
