Um, what? Mechanical trail is very, very well understood.

Do you have any evidence of this? And once again, high speed in a straight line isn't of interest to the discussion.

Ok.
Let me pedant.
Mechanical trail importance in bike stability is still of a disputed importance compared to other factors. That's well evidenced on Internet.
Gyroscopic force applies in equal extents reguardless of wheel size at a given speed if the distrubtion of weight is spread relatively. I may have made that up?

Riding a borrowed Moulton is proof enought to me that they are stable at speed.

Anyway answer to OP is my black 16" mezzo has done 30+ mph on the flat on the A1.
Fast enough.

Let me be *more* pedantic. Mechanical trail isn't a bicycle thing. It is a physical property that has a basic effect on practically every steered vehicle in the world. It is so well understood in terms of stability that entire motorcycle companies are built around it. Heck, Mazda toyed with the suspension system of their 2015 Mazda 3 specifically to add more mechanical trail: they have entire engineering videos about it. Whole caster systems rely on it in industry. The effect of mechanical trail on bike and motorcycle steering stability is exceptionally well understood regardless of what you may have read on the "internet".

I think it's very well established that low trail bikes are much more challenging to control at high speeds except in straight lines and gradual curves. And that *definitely* goes for the Moulton.

But yes, gyroscopic forces have been proven to have essentially no effect in a bike.

Its better stated as an actual measured dimension..

Well I feel like an ass, who would have thought you guys would have been talking over here about the same damn thing for days. Note to self read every trending thread before posting.

Ok well I have stated my 2 cents in my seemingly redundant thread but I will breifly summarize here so I am on the record:

I have 2 bikes near identical geometry, same wheel size, and same tires. One is far more stable at higher speeds much less twitchy feeling and much easier to ride with no hands (i dont usually like to grandstand like that though). The only real difference i can find between the two is the Mechanical steering trail, the smoother one has 45mm of trail and the twichier one has 35mm of trail. All the info I have found online says that most road bikes try to hit the 50mm-65mm trail number.

I should also state that on both bikes though they are both 20" wheels they have very heavy tires (770g maxxis hookworms) which would give them much more rotating mass increasing the inertial gyroscopic effects though I havent notice any significant stability effects on the bike when swapped for my schwalbe kojacks which knock about 1 pound of rotating weight off each wheel.

On a side note I am upset that many bike manufacturers these days and pretty much all folding bike manufacturers don't provide geometry infomation about their bikes. At least armed with a little info you can make some intelectual comparison before you put so much effort into finding a place that you can test a bike or in the case of folders where many times you have no choice but to buy it online.

Well, thanks, y'all. I bought an Origami Crane, still in the 2 wk test drive, but for the most part pretty pleased with it. Riding it I'm experiencing (and thus better understanding) much of what you have been talking about. What should have been obvious--but for me the beginner was not--is that the higher gear ratio in fact means higher energy output to get to those higher speeds. I guess I should have figured that. I maintained about 70 rpm on my old 3 speed comfortably and wished for overdrive. Now maintaining 70 rpm--on the exact same stretch of road--in 8th gear on my Crane is just more work.
Mechanical trail is a concept I have also gotten acquainted with. My Crane "feels" less stable than my old bike, but MT explains why.
Something that no one has mentioned is, uh, maybe the technical term is "over the top"? I.e., when I brake suddenly, I tend to do front wheelies. Thinking about it it, I should have expected that, too, but I didn't. That will take some adjustment.
This is a very educational forum!

Well that tendancy to go over the top is a large component of riding position and possibly a shorter wheel base. I have really learned to appreciate a small road bike seat being able to extend my arms and slide my ass back past the seat to bias my weight back, it took some getting used to but now that is second nature for me.

Xhim has made his choice, but I'm surprised that no-one came on board to mention www.downtube.com - Yan's 9FS is pretty solid all around, and at $499 currently, might have been a front-runner. Confirmation bias: I own one.

Glade the OP is happy with the bike they ended up getting. A bit of banter about tecnical stuff is ok if in good spirit. I learnt a lot here. I also realised my tecnical points were about slow speed stability not high speed.
Re recomeding a Downtube. I did post a photo of one. Nearly a recommendation.

I have hit 55kmh on the flats with my 20 inch wheeled folder... this is where I max out the 53/11 and can't spin any faster. My pleasant cruising speed tends to be in the 30kmh / 18mph range and that applies to pretty much all my bicycles.

The wheel size has much less to do with things than does conditioning and aerodynamics, my folder and smaller wheeled moulton both have drop bars and fit like a conventional road bike,

Put one in Orbit around the Earth, orbital velocity depends on the altitude the Orbit is.