I put an 11/38 7-speed on my Dahon Boardwalk with the original 52 ring up front. That gives me a gear-inch range from 33 to 96. Low enough for my 62-year-old knees in hilly Colorado Springs, and high enough for commuting to work at the same place as my two middle-weight 700c commuters.
The original Neos derailleur could not handle the improved gear range (especially the 11-tooth cog) and broke after a few months. I replaced it with a used. more capable conventional derailler using an adapter.
Here's the story:
https://www.bikeforums.net/folding-b...t-adapter.html