Most of the Chinese I know have never heard of Mandarin; however, they have, generally, passed their Putonghua examination.

Seriously, they do not recognise the word "mandarin," in the context of it being a name for their language. Some, better educated, Chinese take great pride in knowing that Mandarin is the Western name for their language; because, as noted, most Chinese do not.

. . . and I happen to like, "That pasta stuff." As a matter of fact, I often have, "That pasta stuff," here in China. It is quite popular in this region.

Good advice. I've been testing various gears by riding my Bike Friday around using only the same three gears that I would get on a 3-speed Brompton. Currently I am leaning towards the lowest stock gear option (-18%), which is a 44 tooth chainring and 14 tooth cog. What chainring and cog combo are you running, and is that your 3-speed in the YouTube video with the dual chainrings?

Cheers!

Interesting. I would guess that it doesn't take too long to get the hang of downshifting to the smaller chainring. I would also guess that upshifting can only be accomplished using your fingers. Do you have to stop and dismount to upshift, or can you do it on the bike while it's in motion? Either way, it's a strong incentive to keep your chain clean!

At the moment I'm running a 5 speed -- I need to pull a trailer with 2 kids regularly, so the extra range of the 5 speed is needed.

Not my bike in the video.. That's Russ Roca of "The Path Less Pedaled"

It took me exactly one try to get shifting to the small ring to work. You are right that you need to stop to get the chain back up to the big ring. Instead of using my fingers, I constructed a hook-thingy out of welding rod that stick to the stem riser with rare-earth magnets. It took a few attempts to get the technique down, but I can do it in a few seconds now.

I've got a 52 - 39 in the front and a 15 in the back. I haven't worked out what that is in gear inches. (It doesn't matter to me). Pretty much it's a matter of the small ring if the trailer is attached, and the big ring if it's just me. If I've got a longer climb in front of me I'll pop in to the little ring and then swap back up while I catch my breath at the top.

I have been having some trouble with the chain jumping off occasionally when the bike is in the big ring. The chain-line is noticeably off so I'm going to have to swap bottom brackets to solve that problem.

All in all, I like the system fine. It adds minimal weight, and is super reliable. It just needs a little pre-planning when it comes to choosing the correct ring up front.

I'll try to post some pics later of my setup if you are interested.

I've seen other people, using the stock Brompton crank, made by Stronglight, and popping off the plactic guard, then mounting a smaller chainring on the outside, another Stronglight one,

to match the holes in the 50 t stock chainring.. ," greasy Finger shifting" ,
so it doesn't matter if the little ring is on the side nearest the crank arm or not.

Very interesting. What parts do I need to convert my 6sp 44T?

another crank and BB, with a 110 bcd.

Any other dimension/standard I should look for?

The thing to look out for is the inner ring hitting the triangle when the rear triangle is folded. That will determine the shortest bottom bracket you can fit.