So I just discovered yesterday that the mechanism of how bikes manage to stay upright is still up for grabs.
<stuff that would have sounded knowledgable if I’d bothered to wiki it>
For decades the leading theory was that there was some gyroscopic effect responsible. But then it was shown mathematically that such an effect could not produce enough force to resist a rider’s weight.
Then the leading theory was…positive castor? Something to do with weight being in front of the centre of the front wheel. Or something. Anyway that’s been refuted with the demonstration of a bicycle that has a very negative castor – or whatever the opposite is – that is nonetheless stable.
So I was thinking – have we not just made this more complicated that it is?
If I try to turn a corner on a bike, I lean into the corner to help me turn. And I feel a force pushing the bike upright because of the way my velocity is changing.
Could it be that when riding in a straight line, any slight wobbles are immediately resisted as though I were trying to turn?
(Possibly the rider might help this with steering because a bike pushed along with no rider is not very stable…)
It doesn’t balance, you do. There’s a reason people just learning to ride fall over. Once you get used to the tiny cues that your bike gives you that you’re leaning too far in one direction, you correct for them before the shift really becomes visible.
Of course the rider has an important role in balancing, but it’s much easier to balance on a bike the quicker it moves (within reason). It seems to require less adjustment or is it that smaller body movements…or is it that smaller body movements are required for adjustment?
I think I’m right in saying that the physics of this is still debated.
Yes, try balancing on a bike when it’s not moving. Also, how can a wheel balance on its own after being pushed? There is definitely a force pushing it vertically.
You shouldn’t be satisfied with just saying for example: “angular momentum” unless you have a coherent illustration of how it works. Yes it “wants” to continue going forwards, but it doesn’t “know” that if it falls to the side that it won’t be able to do that. It’s not as simple as it may sound at first.
Your theory does not accout for the successful operation of radio-controlled motorcycles, for which kinesthetic cues are not transmitted back to the operator. In fact, the operator can take his hands off of the controls and expect the bike to continue merrily along without falling over.
Something automatic and self-correcting is going on, independent of the rider/operator.
I didn’t want to link the article because I thought people would just say “Dude it’s a humour article – they don’t know what they’re talking about” and not even think whether it’s true.
Also that article does drop the ball somewhat on the gravity entry (pun not intended).
Clearly there’s a quantum relationship between your bike and a separate (but related!) anti-bike in an alternate universe. They communicate using bosons and Avocado’s delicious number. Fortunately, it’s not possible to explain the phenomenon to anyone having less than 2 Ph.Ds in physics, so it’s safe to turn on Jersey Shore reruns until your eyes explode into confetti, which then explodes into candy. Delicious eye candy.
Have fun trying to figure out counter-steering. Basically, on a bicycle or motorcycle, you have to turn left before you go right, and vice versa. I ride both, and still can’t figure out why this is true.
Countersteering is easy to understand. Two issues are at play:
Your handlebar inputs exert their effect at the road surface, where the tires make contact with the road.
If you want to turn, the bike[sup]*[/sup] must first lean into the turn.
#2 is true for any object balancing on its support. A person standing straight up wants to jump to the right? He has to lean right before he can begin moving in that direction; that means picking up his right foot to start falling right, or putting his left foot out to push himself to the right. Hovering helicopter wants to move right? First it has to roll right.
So in order to start a turn on your bike, the first thing you do is kick the tires out from under yourself. Want to turn right? OK, first, turn the handlebars to the left: the tires steer out to the left, making the bike lean to the right. Once you’ve achieved a happy lean angle to the right, only then do you turn the handlebars to the right to actually begin following a right-curving path.
Few bicyclists have ever heard of this concept (and few motorcyclists who have not received professional training), but they all use it. The ones who are consciously aware of the concept and adept at using it are the ones who are best equipped to execute evasive maneuvers that may save their lives someday.
[sub]* By “bike,” I am referring to the combined center of mass of the rider and the bike.[/sub]
I always assumed bicycle balance was from air pressure. Have you ever took something that blows air, pointed it straight up and sat a ball on top of the blowing air? The ball levitates. since the air is moving on each side of it, it doesn’t fall to the left or right. Bernoulli, etc. Same thing with a bike, I thought. Do they balance in a vacuum?
“Gyroscopic precession also plays a large role in the flight controls on helicopters. Since the driving force behind helicopters is the rotor disk (which rotates), gyroscopic precession comes into play. If the rotor disk is to be tilted forward (to gain forward velocity), its rotation requires that the downward net force on the blade be applied roughly 90 degrees (depending on blade configuration) before, or when the blade is to one side of the pilot and rotating forward.”
It’s possible to ride slowly enough so that little to no breeze is created, and it’s possible to ride with the wind at your back, or in a cross breeze. I doubt it’s possible to balance in place during a hurricane.
Not air pressure and not gyroscopic precession. Both of those forces are too small. If air pressure were the cause, how could you balance in even a small cross-wind?
For gyroscopic precession, here’s an experiment you can do. Riding down a residential street, while standing on the pedals, you can easily angle the entire bike 20 degrees or so to the left or to the right, while still traveling in a straight line. If the force from gyroscopic precession was enough to keep you balanced, you wouldn’t be able to do that. It boils down to, a bicycle wheel doesn’t have enough mass or enough angular momentum to do much. You weigh more than the bike, so you can force the bike to lean.
I’ll also point out that gyroscopic precession is not a restoring force. It doesn’t tend to make the bicycle be upright. Once the bicycle is at that angle, it will want to stay at the angle it’s at, so it wouldn’t help you get back to upright.
Hm, when you’re riding a bicycle, you constantly counteract the bicycle leaning to one side or the other by turning very slightly into the lean - that is, if it starts leaning to the right, a slight turn to the right and vice versa. The same cannot be done while standing still because turning into the lean won’t correct the lean unless the bicycle is moving. But you can see it when people are standing still on the bike (or moving very slowly) and are trying to balance - you see exaggerated turning of the wheel.
Gyroscopic precession, positive caster, and user input all contribute together for the effect. It’s not a mystery. Bicycles are unstable, but the degree of instability decreases as it goes faster, because the physical forces play a larger part. But without user input it would fall over. People can develop the skill of staying upright on a bike without moving at all.
ZenBeam, you can’t tilt a bicycle like that without changing the CG by shifting your body. The tilt you are talking about is just your perception of what an upright bicycle is. In fact, based on the CG, the bike is not titled at all. And you could go far more than 20 degrees if the shape of the tires doesn’t take you off course.