Originally Posted by invisiblehand

Your current Dahon has direct drive gearing proportional to ... 20 * 52 / 18 ~ 58
Your 700c road bike has gearing ... 27 * 34 / 32 ~ 27

Your Alfine's gearing ... https://www.sheldonbrown.com/alfine-11.html

The lowest Alfine gear is 0.527. Right now the lowest gear on your Dahon is ~31 gear inches. (27/31) * 52 ~ 45 is the chainring size you're looking for.

42 is a safe bet assuming you care about the bottom end more.