Momentum + Gyroscopic effect
this post was submitted on 17 Sep 2024
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Steering keeps you upright in the same way a broom handle balanced on your hand is kept up by moving you hand around
Gyroscopic effects are negligable
how many licks does it take to get a bike to balance its self? The world will never know!
I'm surprised how much I'm seeing gyro brought up in these comments. It's a factor, but it's practically negligible. It's all in the steering. Start to tip right, and you'll subconsciously steer slightly to the right to correct your balance. Try to ride as slow as you can and you'll find yourself doing these corrections much more frantically and dramatically. The reason for that is because it takes longer for the wheel to roll under your center gravity and "catch" you when you're going slowly so you have to turn in quicker to maintain balance.
Notice that on almost every bike you see, the front axle on the bike is slightly ahead of the neck's axis of rotation. That offset does two things: 1. It stabilizes the steering so that the bike will tend to steer straight and 2. (more important to my point) It makes the balance-correcting effect of steering more immediate and dramatic, making it much easier to ride at slower speeds.
As a counter argument showing why gyro is barely a factor, these exist:
Edit: if you're not seeing the image like I'm not, Google "ski bike".
It's pretty common to bring up gyroscopes for this when people know a little bit about physics. It's all over motorcycle forums, for instance.
As you say, it doesn't work. Experiments have been done where they attach a counter rotating wheel to cancel out the gyroscopic effect, and while it's a little wonky to ride, it works fine.
IIRC, we're not 100% sure how bikes work just yet. Every time somebody comes up with a model that seems to be good, someone finds a counterexample that throws it in the bin. Even your explanation of bike trail isn't all the way there; Razer-type scooters still work without trail on the front wheel.
I figured it was pretty obviously the rider that's making the bike not fall over, not the bike itself.
If the bike's ability to remain upright while moving was a natural feature, then why would you ever need to learn how to ride bikes? You could just sit on it and go if that was the case.
It works on its own. If you push your bike along with a good run and then let go, it'll stay upright until it slows down too much.
Learning to ride a bike is mostly about being confident enough to let the bike work itself out. It gets more stable as it goes faster, but it's natural to be afraid to go faster when it already feels unstable at low speed. Then there's a little bit to learn about countersteering, but most people figure that out without being told it's even a thing.
Yeah. Case in point: Ghost riders in Motorcycle racing.
Motorcycles also tend to fall down when stationary, yet stay upright without the rider at speed.
Also makes me wonder if just the bike crossing the finish line would be enough to win if you fell off in first place just before the line.
Then why does going faster also make it easier to balance on something without steering, like a snowboard?
My assumption is that when you're standing still relative to the ground you can fall in many directions, but once you start moving momentum limits the directions you can fall to the ones in line with your motion. So the faster you're moving the fewer directions you need to worry about.
Snowboards definitely have steering, you twist the board and shift your weight to manipulate how the edges contact the snow, it's just not quiet as explicit as a bikes front wheel. But whether it's a bike, a board, or literally any moving thing on land, the steering happens because you applied a lateral force to the ground and an equal and opposite force was applied back to you.
The snowboard uses different methods of applying that force, but other than that it's the same concept as described in my first comment: Greater speed allows more subtle corrections to take effect more quickly.
Now the snowboard does have a wider contact area with the ground, but that really only helps you on flat ground at very low speed, or standstill. Advanced boarders will carve transitioning from edge to edge most of the time.
I don’t get it when people (usually chavs) can just sit back with their hands in their pockets - when I try it my handlebars twist out to one side instantly.
Most bikes are stable and a cyclist can weight shift to turn gently without touching the handlebars
Mine is a recumbent that steers with long handlebars. The handlebars prevent the bike from balancing itself.
Yours might have barely stable geometry, or badly placed weight on the handlebars
tf is a chav? This is a thing I do and I'm not from anywhere that has the term "chav". I've seen lots of cyclists do it.
As with regular cycling, the rider is doing microcorrections to keep the bike upright. You can do those corrections with a lot of leverage using the handlebars, or you can do it with less leverage using your core muscles. Concentrate on holding in your core and you'll succeed. It's also much easier at higher speeds (downhill, for example) for the same reason that steering a bike the normal way is easier at higher speeds.
Brah just discovered conservation of angular momentum
It's not that. Gyroscopic action exists of course, but it's fairly weak against the weight of your body. Balancing a bicycle is just like balancing an umbrella on your finger, except you can easily move your finger any direction you need. To move the bicycle sideways, you need to already be moving forward.
~~it really is that though, have you not done the rotating wheel experiment? it is fucking hard to tilt the axis of a wheel rotating at a speed which is comparable to biking speed.~~ come to think of it maybe not:
Track stands! Not a contradiction to your statement at all though: you need to be moving just ever so slightly.
With a fixie it's easy, because you can pedal forwards and backwards in tiny amounts. With a freewheel, it's trickier but you get the hang of it with practice. Ideally you'll have an incline, so you pedal forward to go forward, and ease up to slide back. After some practice I can use the raised reflective paint from e.g. crosswalks as the "incline." This miniscule motion is enough to balance
and like you said, it ain't the angular momentum that does it.
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Can confirm. Last week, I got home from a ride, stopped in front of the garage, couldn't unclip, and promptly fell over. It turned out one of the bolts fell out from the cleat during the ride, so the cleat just rotated, instead of unclipping. D'oh. Fortunately, I mostly landed in grass, though I did scrape my ankle a bit.
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Fuckin magnets
How do they work?
But pedaling on a treadmill make you fall over.
What the hell?
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first, and less importantly, your wheels are gyroscopes
second, and much more importantly, at speed you use your steering to compensate for imbalance. You lean a little right? slight steering to the right compensates. When standing still, steering is no longer an option (duh)
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Gyroscope effect. You ever do the experiment where you spin a bike tire really fast and then try to tilt it? Shit's nuts.
That only causes part of the effect, most of it is the bike's steering countering the momentum of your fall.
You wouldn't be able to balance on a bike with just the wheel spinning, you're too heavy. That is why bikes on those indoor rollers allow the bike to move left and right a bit.
Just wait till OP learns that you need to counter-steer bikes to balance
That's always fun. Some people will swear it can't possibly work like that, but they have plenty of experience riding bikes. You wouldn't be able to turn properly at speed unless you're counter-steering, so they clearly have done this. The idea seems to be so incredibly intuitive that people don't even realize they're doing it, which is very interesting.
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Same principle as a gyroscope: a turning wheel will tend to stay perpendicular or parallel to the direction of the gravity vector because if it starts tilting away from such orientation there's a force that pushes it back.
Also works better with bigger wheels (if I remember it correctly the effect is related to spinning momentum).
I was pretty surprised when learning Physics and they show us how to derive the formula for that (which I totally forgot since that was over 3 decades ago).
Edit: Actually the gyroscopic effetc is just a part of it. See this article
Gyroscopic effect is not even significant. Lock your steering and you will fall over no matter how fast your wheels are spinning. (Which can happen with a badly pitted headset)
Actually, it's the bike's geometry rather than a gyroscopic effect. Try rolling a bike backwards rather than forward - it'll topple quickly
Yeah, you're mostly right: Why bycicles stay upright.
There's some gyroscopic effect, but per that article it's not the main reason.
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Freestyle BMX riders go in reverse all the time and they don't fall over.
Having the pivot point (steering) for the front wheel behind it's axle helps
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