So I took the plunge and got a 39T chainring. It did feel great on the one short uphill I tested it on - need to do a real test!

At first I didn't shorten the chain. The derailer took up the slack nicely, but the overlap made it impossible to backspin the crank while folding the bike to attain the proper orientation of the crank arms - unless you fiddle with the derailer by hand.

Hilarity ensued thusly:

1. I reasoned, 50T - 39T = 11T, so I need to remove 10 links.

2. With 10 fewer links, the bike folds, but doesn't unfold!

3. Realized that I'm an idiot and I should only have removed 5 links.

4. Unhook the master link.

5. Accidentally let go of one end of the chain. Have the derailer whiplash back, sending the master link flying off under the wood pile in my workshop.

6. Sigh. Add back the links by hand, close the chain by hand.

7. I'll wait until daytime, or a day when I'm feeling energized, to hunt for the master link under the wood, paint cans, and assorted detritus in *that* corner of the workshop.