This is an interesting discussion for me as I have both 16" and 20" folders. I specifically choose the bike for the purpose at hand but I realize many people don't have that luxury. Hands down the Brompton in the 16" wheel size rides vastly superior to the other 16" wheeled models out there. It crude but semi-effective rear suspension takes the edged off most bumps rather well. However compare it to a DT or my full suspended Dahon and there is NO comparison in ride quality. It definitely doesn't ride as well as my Swift with Big Apples on it (even with them at higher pressures and not for best comfort).

It is fairly close to a normaly 20" bike running 70psi tires (5bar). One think I definitely notice is that the smaller tires are terrible if I need to ride across grass or anything other than hardpacked dirt or roads. They are about as bad as the Stelvios in 20" size on my SpeedPro.

Biggest downside to almost all of the 16" bikes is they weigh almost the same as the 20" wheeled versions. Only is the Brompton really a significantly smaller bike than the other 20" to really matter. It will just squeeze into my 28" suitcase without disassembly for overseas travel. With a little work my 20" will fit into the same suitcase AND weighs less than any of my Bromptons.

I have noticed also on gravel and cobblestone streets the 16" tires are definitely worse than the 20's. Also there are far FEWER tire choices in the 16" size as well. Gearing also becomes a major issue too. Big potholes are more of a concern as well as rail crossings. Rims wear more quickly, braking can be less effective and a whole host of other issues that are more common on 16" models than their 20" counterparts.

So far the most I've ridden my Brompton was a 50 mile stretch and that was enough for me. Mostly I was hampered by the limited gear range more than anything. My general usage is the Brompton in very congested cities and my "bigger" bikes for city riding where I won't be a lot on buses or metros as well as any time I really want to tour while traveling. My Swift is far better to tour on my Brompton as I have a wider gear range, better seat and bar relationship and more more room for luggage. The ride quality is defnitely better but I think the ride quality of a Brompton would surprise a lot of people in a good way just like their crappy brakes will surprise people in a very negative way.

By comparison the Dahon 16" models are toys. Only the Presto Lite is really a semi-serious model. It is at least light weight but it might be fragile in the long run. Of course they cost less than the Brompton too. This is one area where Dahon could do much better than they do. While I am FAR from being the world's biggest Brompton fan, they do own this segment of the market.