I have a new-to-me Motobecane Team Champion, and it came with a ridiculous corncob, I think 13-18 six speed. I have been futzing with it trying to get a manageable gear--- made more difficult by the (otherwise lovely) Simplex SJJ 6600 derailleur, and the 144bcd chainring size on the (otherwise lovely) Stronglight 107 cranks. Dropouts are Simplex.

The published 24t sprocket limit on the rear derailleur, and the real-world limit of a 42t chainring was pretty tough for the mountains in my neighborhood in Vermont--- just getting back up my driveway at the end of a ride means 100 feet of 12+% gradient~!

Based on the info in this thread, I've been trying to get a 14-28 freewheel to work--- and it does, kind of. Right now just a cheap-looking Shimano TZ500, but someday something more vintage/nicer. The upper pulley rubs slightly on the sprockets when in the two lowest gears--- didn't stop the bike from working, but audible and not good in the long term, I bet. I found that if I move the rear wheel back in the dropouts quite a bit I can get enough clearance and noise-free operation. Not to the point where I had to remove the axle adjustment screws, but pretty much at the travel limit for those screws. Any downsides in doing this?

42x28 is still pretty tough, but it will at least let me ride the bike without walking most of the time....

Thx,
N