I suspect that nobody thought of a 2 wheel design because nobody thought it would be stable. The hinge between the front and back wheel is crucial. Even today, few bicyclists understand how a bicycle is able to turn and remain upright.
None of the early designs seemed to have any brakes, making them quite impractical.
Without modern steel and machined parts, a bicycle of wood and iron would simply be too heavy.
Maybe there would have been an opportunity for a three-wheel recumbent bike to be developed first? Seems like a lot of easier engineering if you can take stability as a given and just worry about the driver supplying direction and power.
Eh, doesn't work well with the factors that led to the penny-farthing.
The penny-farthing was a direct drive on the front wheel - no chain. It had you positioned on top of the wheel to get as much traction as possible.
A primitive recumbent trike would tend towards the same design, like a child's trike, with no chain and a direct drive on the front wheel.
And because you'd get terrible traction, with so little weight, you'd be dead in the water until the machining was available to engineer a chain system to connect pedals in front of the cyclist with wheels underneath. I don't think there's any penny-and-two-farthings intermediate to make the recumbent trike work before that.
Here is a simple simulation of a bicycle's stability [1]. The simulation more or less predicts what happens in real life, so we do understand why bicycles are stable.
As you can see from the simulation, this is a multibody dynamics problem. The bicycle and human have lots of moving parts, and as they move there are forces in 3D [2] amongst them. So there can't really be a simplified, short and mostly complete English explanation (like for why planets go around the sun). That doesn't mean we can't predict.
> Their study shows that there isn’t one simple reason for this phenomenon. A combination of factors, including gyroscopic and caster effects, bicycle geometry, speed, and mass distribution come into play to keep an uncontrolled bicycle upright.
I think we’re saying the same thing. There is no simple physical explanation that humans can intuitively understand, because the interaction of forces is so complex. I’m not claiming that it’s a mystery causing fundamental problems for physics.
Actually the intuitive human reactions on a bike are often the exact opposite of what you need to do to balance the bike. F.ex. if you look at kids learning to bike their intuitive reaction to the bike falling to one side is to lean to the opposite side, but that has the exact opposite effect of what they want to achieve. When you lean to one side you exert force force on the bike the other side and the bike will fall quicker. What you need to do is to use the handlebars to turn a little bit to the same side the bike is falling to re-balance it. Ehm, at least I think so? The more I think about it the more uncertain I become.
Let me restate. There are many natural phenomena that are complex. Say the details of interstellar nuclear reactions connected to the behavior of stars. There is no simple explanation, only complex mathematical models that predict the behavior very well.
So don't say "no astrophysicist understands stellar reactions" because that is false. They understand fully, and can write the model and simulate it to answer any question.
Ditto for bicycles. Just because there is no simple explanation for bicyles does not mean we don't fully understand the physics of bicycles. It just can't be put in English. Only in complex mathematical models.
> no astrophysicist understands stellar reactions" because that is false
Cyclists are not exactly the equivalent of "astrophysicists" in this situation though. There are of course physicists who are also cyclists, but basically no cyclist who is not (or isn't very interested in the field) would be able to explain it.
>> There are of course physicists who are also cyclists, but basically no cyclist who is not (or isn't very interested in the field) would be able to explain it.
This is probably a case where not being a scientist was an advantage. Turns out they didn't need a simulation or mathematical proof it could work in order to try it.
The amount of detail on that site is breathtaking. Beautifully done, really.
However, on the question at hand, it mostly says:
>Bicycle stability can’t be explained using just one or two mechanisms. It’s a combination of many different intertwined factors, like the mass distribution of individual components, size of the tires, geometry of the frame, and others.
[...] What keeps bicycles balanced with or without a rider is still an active area of research, and even the seemingly basic idea that, for a bicycle to be self-stable, it needs to turn the handlebars into the fall, has not yet been proven.
After looking at that page, I understand something, but I am still curious about other things.
There is no mention of air resistance at all. Does it play a role in (de)stabilizing the vehicle in higher speeds? Would a bicycle work as well in, say, lunar vacuum (I imagine that it would be hard to pedal in spacesuit, but let's assume a spherical cow and a lunar bicyclist in normal clothes). Would a lunar bicycle be more stable at lower speeds because of the lower gravity on the Moon?
Motorcycles and bicycles turn with the same principle: countersteering.
When I started riding motorcycles, I bought a well-known motorcycling book. It had a whole chapter on countersteering because there are even today many seasoned motorcyclists who don't believe or understand that you turn using countersteering.
You're answering the wrong question. The question is not "how does the rider initiate a lean" which is usually through countersteering.
The actual question is "Why, when you give a bicycle a good shove, does it stay upright on its own, continually changing its direction to balance itself?"
The counter steering answer to that question is rake, the fact that the steering axis hits the ground in front of the contact patch if the front tire, so that when a bike is leaned over it self-steers into the turn (the contact patch torques the wheel around the steering axis) and countersteers itself upright.
It's well known in motorbikes that the amount of rake is what makes a bike more stable vs more responsive to steering. Some folks lower the front of the bike - tighten the triple tree lower on the forks - to increase responsiveness on otherwise more boring bikes.
Of course there's more to it all, gyroscopic effects and so on, but this is the countersteering perspective.
Reviewing this comment I didn't get all the terminology right - when I said rake, I was conflating trail, rake and steering head angle, where the latter two combine to define the amount of the former.
It's also amazing how stable a bicycle is, that it allows you to steer with one hand or even "look ma, no hands". I only came to appreciate that after I started riding e-scooters - those are very hard to control if you don't keep both hands on the handlebars, and taking both hands off will probably throw you off instantly.
Yep, e-scooters are maybe 7 years old (I start counting from the release of the Xiaomi M365) and so it’s real a shame that e-scooters with turn signals are finally here since only one year or two.
Back when I used to do my commute with e-scooters, indicating my direction was a real pita and, most of the time, totally impossible. In fact I used to use the sidewalk and pedestrian crossings if I needed to go left through the traffic.
Probably on the same percentile as the number of people that understand how the Otto cycle works to power their car, or how differentials in the axles function to apply said power to the wheels through turns, etc.
Understanding the physics is not a requirement to operate the vehicle.
It is simple. A bike will be stable without a rider because if it tilts to the left, the front wheel will also tilt to the left (as the hinge is behind the center of gravity). This results in a left turn, and the centrifugal force of the turn will bring the bike back upright and straighten the wheel.
The rider turns the bike by moving the handle bars slightly in the opposite direction he wants to turn. Then the bike falls in the direction he wants to turn, and the handle bars are then rotated in that direction. To straighten out, the handle bars turn a little tighter, and the centrifugal force of the turn pushes the bike back upright.
Simple? No. But the universe is not a simple place.
Definitive explanation? Yes - to a significant degree of definitive. As with all science/engineering-understanding there are always further details but this we've got pretty well down at the macro level humans operate at.
Nobody would think walking is as stable as we know it is (try to put e.g. a Star Wars action figure in standing position on a table, it is not so easy and not very stable).
Also, horses are the original self-driving transportation, and anyone with the means to buy some newfangled technology like the early bicycle. It's been a hundred years and we're still not better in that regard than the finest of equine hybrid technology, so can you imagine the landed gentry giving that up to... Exert themselves to travel to town?
Yup... before the industrial revolution, those who could have theoretically afforded a bicycle (and had a need to transport only themselves to somewhere else) could also afford a horse, while all the others not only couldn't afford a bicycle, but also had no need for one. Peasants barely left their village, and if they did, it was to deliver some produce, either to their landlord or to the market, and for that a bicycle wouldn't have helped...
None of the early designs seemed to have any brakes, making them quite impractical.
Without modern steel and machined parts, a bicycle of wood and iron would simply be too heavy.