Comment by Gigachad
4 days ago
At some point I saw someone put a counter spinning wheel on a bike to negate the gyroscopic effect and they were still able to ride fine. I'm not quite sure how to describe it, but there is something about the geometry of a bike that is sort of self correcting. You can ride a bike without touching the handlebars at all, and you can even steer some amount.
Here's what I originally typed out before googling:
The "something about the geometry" is called caster, and is the same effect that makes the front casters on a shopping cart go straight: the point where the steering axis intersects the ground is ahead of the contact patch of the tire. On a bike, this is mostly determined by the angle of your head tube when looking at the bike from the side (if the fork is "bent" from the side view, this would also contribute to the caster effect).
But I've now googled, and found a paper that says that a bike can be stable without gyroscopic or caster effects [1]. It seems like the specific mass distribution of the steerable mass (front wheel, fork, handlebars, etc) vs the rest of the frame matters, and of course all of these variables interact in complex ways. They do agree that caster plays an important role though.
Vehicle dynamics is notoriously tricky stuff. I can say with experience that it doesn't get easier when you go to four wheels.
[1]: https://www.researchgate.net/publication/51051995_A_Bicycle_...
> but there is something about the geometry of a bike that is sort of self correcting.
Yup. Plenty of videos on youtube where they send a bike down a hill with no rider and as long as there is forward motion it will self-correct and stay upright.
Bikes in motion are self-balancing, and with no rider on, will continue indefinitely until the forward momentum has been exhausted.
https://www.youtube.com/watch?v=NcZCzr9ExKk
This is because gyroscopic forces are not significant except at high speed, and most of the forces relevant to cycling and which direction the bicycle goes are generated between the front tire and road surface. Turning the handlebars to change direction is also only relevant at low speed for the same reason.