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Comment by bambax | Hacker News Reader

> Bicycles achieve balance through the gyroscopic effect, something with angular momentum and physics or whatever

Bicycles achieve balance because the rider counter-steers to prevent the bike from falling aside.

Destin from SmarterEveryDay had a friend build a special bike where the actions of the handlebar are inverted: when you turn it to one direction, the front wheel turns in the other direction.

It's impossible to ride such a bike.

Well, not exactly impossible: you have to completely re-learn riding, like you never knew before. Which shows that steering is the core (only?) skill to riding.

It's a great video: https://www.youtube.com/watch?v=MFzDaBzBlL0

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>Bicycles achieve balance because the rider counter-steers to prevent the bike from falling aside.

This is only partially correct. A rider can compensate for road irregularities to keep the bike upright, where an uncontrolled bike would topple over, however an uncontrolled bike is stable when rolling on flat terrain. That there exist bikes that, by making countersteering impossible are unridable, doesn't support the proposition that countersteering is the primary mechanism by which a bike stays upright, it just shows that countersteering can have a much more powerful effect that the dynamics of angular momentum.

More on the physics of how bikes work, Derek Muller from Veritasium demonstrated what happens if you lock the steering of a bike: https://www.youtube.com/watch?v=9cNmUNHSBac

> Dustin from SmarterEveryDay

I think his name is Destin: https://en.wikipedia.org/wiki/Destin_Sandlin

Thanks! Corrected!

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.

I saw that SmarterEveryDay video and it's a crazy thing to do but fun to watch.

Terminology: balance is from steering (not counter-steering aka push-steering) which is to get the bike (usually motorcycle) to lean faster which allows taking a corner sharper. To balance upright, one steers the bike in the same direction the bike would naturally steer (as it's falling to one side) by the way the forks are raked/offset.

https://ciechanow.ski/bicycle/

As a motorcyclist, counter-steering is a very pronounced and useful feature. I've tried employing the same technique on my bicycle and it had no effect. I'd be keen to understand others experiences of countersteering on a bicycle.

I too am a motorcyclist (and now, mostly, a cyclist) and think I may have misspoke (steering vs counter-steering).

When I learned to ride a motorcycle I was taught to push the handle bars with the hand on the side I wanted to turn (so, if trying to turn right, push with the right hand); this causes the bike to "fall" on the side of the turn, and follow the turn.

This is what I meant by "counter-steering" but 1/ it only works at relatively high speeds (above, say, 20 mph, which isn't high on a motorcycle, but pretty high on a bike) and 2/ it doesn't "prevent" the bike from falling, it makes it fall, which is what we want.

Following the same principle, staying upright on a bicycle involves steering, not counter-steering: when a bike starts falling to one side, turning the wheel to that side makes it want to fall to the other side; and if done fast enough and often enough (as all riders to), maintain the bike upright.

> This is what I meant by "counter-steering" but 1/ it only works at relatively high speeds (above, say, 20 mph, which isn't high on a motorcycle, but pretty high on a bike)

No, it works at much lower speeds. This guy is not going 20 mph: https://upload.wikimedia.org/wikipedia/commons/5/55/Counters...

yes, this is what counter steering means to me too.

Can you clarify what is it exactly that you consider counter-steering?

My understanding is that it means "briefly turning the handle-bars to point the front wheel in the opposite direction of the intended turn, causing the vehicle to start tipping over in the direction of intended turn", which is exactly how you steer both motorcycle and bicycle.

Counter-steering is how bicycles steer, whether you're doing it consciously or not.

Maybe the description the author found was describing a tendency of a riderless bike to stay upright? Counter-steering is involved there but I’m not sure it’s the most significant bit. That is a good video though!

What's fascinating to me about that video is that when he learned to ride inverted, he LOST the ability to ride directly. There's some switch in our brains that can get flipped

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