JDme Earlier this year I bought a used 2007 Dahon Boardwalk 7-speed folding bike and have been having a blast.
I converted it to bull-horn bars. I regularly ride it 10-12 miles and have done 35 miles. Here's a list of the mods I did:
https://www.bikeforums.net/folding-b...lk-mods-done-n, ow.html
I also have a 26-inch drop-bar mountain bike and two 700c road bikes. The 20-inch is comfortable and fun in some ways the bigger wheel bikes aren't. It's nimble even though it it heavier than my one roadbike, and weighs the same as my commuter, but he center of gravity seems to be lower. In a straight line it feels about the same as the other bikes since they now all share the same riding position, and with the upgraded gearing my average speed on it is similar to my much heavier MTB commuter Utility bike, which is about 7/8ths the average speed of my road bikes. (13.5mph roadbike avg versus 11.5 mph for the MTB and 20-inch folder.
The 26 and 700c bikes are less "twitchy" than the 20-inch and my 700c Charge Plug commuter, with its longer wheelbase and relaxed geometry tracks the straightest and smoothest.
I find that the steering column on my 2007 Dahon Folder needs tightening from time to time, including the "cleat" thing at the folding hinge. (but not too tight or it won't latch). Also because it was designed for minimal torque from the original straight bars and not the increased rotational torque forces of the bull bars, I also find I have to tighten the bar clamp quite a bit.
Although I have smooth road tires on the Folder, they are not as supple as the tires on my three other bikes, and the higher rolling resistance is noticible from time to time.
One other thing I think about is how to lock up the folder. Since the seat post has a quick release, I run the cable through the seat rails, as well as the frame and wheels (which have non-quick relase nuts and nut covers). This means I need to drop the seat in order for the cable to reach through all three. However, when folded I merely do the seat rails and frame since it would take a great effort to undo the wheels.
But you know there are 26" folding bikes out there, like Montague, Columbia and other brands. They certainly don't fold as small as a 20-inch or smaller diameter folding bike, but they probably feel more familiar while riding.
I was a serious bike commuter for 28 years, with a 9 mile commuter each way. If I were to resume that commute and had to use a 20-inch folder due to space limitations, based on my experience the last few months with my older Dahon, I think I would be happy with just an upgrade to the tires, and front chain ring. I would like to get just a little higher gearing for faster cruising, but I'm happy enough with what I have now. The stock gearing was not low enough for the hills of Colorado Springs, and the original high gear was not high enough for cruising at the speeds I want, but then, that was the case with my other bikes as well.
Oh, and speaking of gearing...I never thought I'd be happy here in the hills with just 7 speeds, but with the wide-spaced ratios I now have, it seems to work for me...for now.
Like any other bike, a cheap folding bike will be heavy, with finicky gears and brakes and could be less fun to ride than a lighter bike with better components.
One last note...because of the folding mechanisms in the frame and steering column, and the extra length of the steering column and seat post I doubt my 20-inch folder would hold up to some of the unexpected curb strikes and pot holes I have experienced over the decades. I may be wrong, but I haven't encountered any yet, so I don't know.
But the bottom line is this: My 20-inch folder (with modifications) is as capable a commuter as my three other bikes and just as fun to ride, although it may not be a sturdy in extreme cases.
Hope all this helps your decision either way.