I have a very nice bike that I built from a vintage new steel frame, threadless bottom bracket (because of the french thread in the frame) and 110BCD crankset. It is currently mounted as single speed, and I would like to add a rear derailleur.
The dropout spread is 125mm and the current chainline measurement is 45mm.
I have many questions and try to evaluate the feasibility. I would like to keep as many parts as possible, in particular not change the bottom bracket because of the odd standard (and the fact the thread is in part damaged).
I am contemplating the SRAM 1x solutions, but I don't know if 11 speed compatible wheels will fit the 125mm dropouts.
I suppose I could pick a 9 or 10 speed wheel (would they fit?), and add a 9 or 10 speed rear derailleur, but I am not sure of the chain line that is required.