Quick Addendum...

I've been reading up more on touring on folding bikes today. It's quite the popular pass time in the UK it seems where folding bikes are much more popular. I was worried about parts availability if on a long tour and didn't have enough supplies to make repairs on the road...but I learned a few things that are causing me to change my mind.

Bikes with 20" tires (unless a 'high performance' folding bike) will take standard BMX tires unless they're super knobby...available everywhere. Same with tubes.

They use standard gearing hardware usually made by a major brand name like Shimano so service and even replacement on the road is a possibility. They usually only have one ring gear so there's less to go wrong. Some have geared hubs which are expensive but ultra low maintenance.

Brakes are usually standard so sourcing pads on the fly is also a possibility.

Frames are usually made from Aluminum unless it's a model from the 70's or 80's. This means you can't get a broken frame welded in the middle of nowhere by a local...but if you got some of those good 'miracle' aluminum brazing rods you could make repairs sufficient to get you home and all you'd need is a torch and a few basics...you might even be able to carry it with you in your tool kit. I've used that stuff on Motorcycle sub frames and it was more than strong enough to get people home.

Most of them have 6 or 7 gears (some have more, some have 1). This means that there is usually no true 'granny' gear for getting up steep hills. If you stick to paved roads this shouldn't be an issue unless you're loaded down and/or on some crazy mountain passes. I was surprised to learn that even the slightest folding bikes usually have a capacity of at least 200lbs. The one I'm looking at tonight is supposedly rated for over 240.