Look, everything works better when it fits right. We're fortunate to live in an age of frame sizes in what, 8 or 10 sizes in 2cm increments in road bikes (at least it used to be), and at least small/medium/large/extra-large on other large-wheel bikes. I'm fortunate, my folder fits me dandy. It's supposed to fit 4'8" to 6'3", but I know that is mostly the seatpost, handlebar height and particularly reach are a whole 'nuther issue. The diverging seatpost and handlepost helps, put both up (with an adjustable handlepost) and the reach is longer. Bike Friday tried to market to schools, a 20" non folder with a telescoping monobeam frame (concept later used on the Haul-A-Day cargo bike first gen). I saw on here months ago, a folder with a very short frame, and I derided the handlepost setup (which I regret) because I couldn't see the logic of it jutting way forward and then up, instead of directly up; Now I realize that is to allow knee clearance when standing on the pedals, while allowing a very compact frame length. But, weight distribution will not be ideal.
For every height, amazingly, there is a folder available that fits. Wheel diameter might need to be proportional, might not. Geometry might need to be fine-tuned at size extremes. Bike Friday laudibly will build frames for very short-statured, up to NBA-center-tall, a bit easier for them because every frame is made-to-order locally, one of their pluses.
I'm a sailing enthusiast. Never owned a large keelboat. But I've read a standing-height stack of books on the subject, some by famous designers, some by marine architects, and looked at the specs of hundreds of boats on sailboatdata.com, and have reached a point where friends in the market ask me about a particular model, and if the specs are published, I can look at the numbers and tell the person about this boat, in relation to others.
For bikes, if you know what you are looking for, and the bike geometry numbers are published (that's the hard part), you can get a clue from those. But it can be tough comparing bikes with different wheel sizes; Smaller wheels, you think less gyroscopic inertia, so you would think you want a bit more fork trail/caster to compensate. Except, that can make the steering heavy when loaded, and cause more wheel-flop.
Ref: Good reads:
https://en.m.wikipedia.org/wiki/Bicy...cycle_geometry
https://en.m.wikipedia.org/wiki/Bicycle_fork
The purpose of this offset is to reduce '
trail', the distance that the front wheel ground contact point trails behind the point where the steering axis intersects the ground. Too much trail makes a bicycle feel difficult to turn.Road racing bicycle forks have an offset of 40–55 mm.
[2] For
touring bicycles and other designs, the frame's head angle and wheel size must be taken into account when determining offset, and there is a narrow range of acceptable offsets to give good handling characteristics. The general rule is that a slacker head angle requires a fork with more offset, and
small wheels require less offset than large wheels.
That last part, less offset, so more trail: The smaller wheel radius means a vertically shorter triangle at the road, so inherently less trail with the same offset. So to get similar trail as larger wheels, less fork offset, a "straighter" (or less angled if straight blades) fork. Put taller section tires on the same fork and wheel? Vertically taller triangle at the road, trail increases (and vice-versa).
Correspondence from Bike Friday in response to my questions regarding differences All-Packa versus New World Tourist:
The All-Packa has ~7mm more geometric trail through 5mm less offset, 4mm more axle-to-crown and .3-.5 degrees slacker head tube (depending on frame size) than a NWT fork. As you note, pneumatic trail would vary by tire. In my testing, there is little discernable difference in handling for tires less than 50mm wide, but the changes prevent excessive oversteer with wider tires.
I'd prefer to focus on the difference in trail between the bikes, as our trail numbers are intentionally much lower than the trail numbers for larger wheel bikes and tend to be misinterpreted as being "low-trail".