cooker

Because the bike can shift side to side as you ride, thus staying below your centre of gravity.

Gyrostapo

Which can stay upright at the slowest speed - a riderless bike, or bike and rider? Gyroscopic forces don't help when you're riding at 4 mph.

catatonic

Maybe so, i just woud like to have the final verdict on what the determining factor is though, since gyroscopic force seems to not be as important as I thought it was.

Inertia combined with genter of gravity?

I really don't think it's the rider itself....just sounds a bit too out there.

DannoXYZ 

Yes, it's the rider, gyroscopic effect is irrelevant. The part that really makes the bike work is the front-end geometry with steerable front-wheel with headtube-angle and fork-offset(rake). There are two mechanisms at work, for low-speed and high-speed.

At low-speed, you want to keep the COG (body+bike) centered between the two contact-patches. This is like balancing on two-feet, balancing on a chair tipped sideways onto two legs, balancing on a ladder that's vertical, etc. When you turn the steering back and forth, you're moving the contact-patch in front laterally in an arc. This moves the line between the contact-patches laterally to center the bike underneath your body. This is why you need to saw the steering back and forth so much as you come to a stoplight at low-speeds, and also how balancing on rollers work. This throws your COG off to one side of the line between the contact-patches and the bike+rider starts leaning to that side:



Notice that when you steer to the right, you will actually end up leaning left due to two forces. One is due to the opposing lateral force from the ground to the steering-effort; it pushes back on the tyre, the bike and you in the opposite direction that the contact-patch moved. And the other force is vertical due to gravity, which pulls you down towards the side that the COG is offset over. The net of effect of these two forces lateral+vertical is you end up leaning in the opposite direction of the steering-aim.

Another way to maintain balance at low-speeds is to keep the steering fairly straight and lean the upper-body to one side or the other. If you start falling to the left, you move your body to the right to keep the COG over the contact-patches. Most people do a combination of steering-inputs and body-movements to maintain balance and a straight line at low-speeds.

The reason highly-skilled riders can ride really slow in a straight line and not fall over is they keep their COG centered (body steady) between the tyres' contact patches and make very quick and minor corrections often. They wiggle their butt and legs while steering small amounts when they sense a tilt/lean coming on and they can sense this sooner and make corrections faster than new riders.

DannoXYZ 

At higher speeds, imagine a static system of a bike+dead-weight on the seat that's in perfect balance and moving along at 20mph like in the "Perfect Balance" picture above. It will continue to stay perfectly vertical and straight in the absense of outside forces. Only wind resistance will slow the bike down longitudinally and external sideway forces will cause it to lean laterally.

Now if any of you watch the 250/500cc MotoGP on TV or have ghost-ridden your BMX bikes as kids, you'll realize that a bike is in perfect balance and harmony at speed and will ride by itself! After many motorcycle-wrecks on the track, you'll see that the motorcycle continues on in a perfectly straight line after it's thrown off the rider... sometimes it takes out the advertizing banners of the opposing teams with exacting precision...

This is similar to the simplest higher-speed case with a bicycle: coasting without pedaling. You'll notice that the bike rides a perfectly straight line without much steering input. You can even ride no hands easily and the front-wheel tracks straight. This is similar to the earlier example of the dead-weight on the seat in the "Perfect Balance" or the riderless motorcycle; the bike will ride a straight line without any inputs needed. So... given that the bike will ride a perfect line by itself or with a dead-weight, we'll have to conclude that it's the organic creature piloting the bike that makes it change directions or even crash.


How that occurs is through the front-end geometry with the effects of caster-trail that's created by the headtube-angle and fork rake/offset... similar to a shopping-cart:

The trailing contact-patch of the front-wheel behind the pivot-axis is what generates stability and aims you in a straight line and keeps the center-of-gravity between the contact patches. The forward-momentum of the cart or bike+rider generates an equal force in the opposite direction on the tyre's contact patch pushing backwards by the ground. Since the contact patch is offset from where the pivot-axis crosses the ground, the backwards push of the ground tends to rotate the wheel's contact patch BEHIND the pivot into a "trailing" position which aims the wheel in the direction of travel... The larger the trailing distance, the stronger the centering and stabilizing effect....

This is the "what" of the situation and we've seen this a thousand times... next I'm gonna tell you "WHY" and "HOW" it works...

DannoXYZ 

... next up... we'll go over dynamic balancing tricks... pedaling motions that cause bike/body lean and shifts of COG, and the steering-corrections needed...

Trsnrtr

I've always been amazed that even a child can dribble a basketball at full speed, pull up, move right or left, and pop a 15 foot jump shot and get nothing but net. Consider the physics and brain complexities going on there.

skiahh

OK, while this zero gyroscope bike proves that it's not exclusively gyroscopic forces that keep a bike upright, at higher speeds, it most certainly doesn't DISprove the notion that they do contribute. Of course there is a good deal of the human balance reflex involved, especially at slow speeds or while trackstanding or trials stuff.

But at high speeds, the gyroscopic effect is very strong on bikes, the faster the stronger. Isn't countersteering a good example of the gyroscopic forces and precession at work on a bicycle or motorcycle? I know from experience that iIt's harder to initiate a turn at 100 MPH on a motorcycle than at 50.

cooker

The problem with gyroscopic forces is that they aren't smart enough. Once the bike starts to tilt, gyroscopic forces would tend to keep it tilted. yet if you ride along in a straight line with your bike tilted, it fights you. Gyro forces should be helping maintain that tilt, yet they seem not to help much.

Those wheels are way heavier and going way faster than bicycle wheels, so perhaps gyroscopic effects make a bigger difference here.

The fork rake is designed so that if the bike tilts, gravity forces the wheel to turn in that direction, even when stopped (try standing holding your bike by the seat. If you tilt it left, the wheel turns left). At speed, gyroscopic forces supplement that fork effect, so gyro helps steer the bike back into an upright position as it starts to fall to one side. However those gyro forces don't know exactly when the bike has returned to a vertical position. It's the gravity effect at the fork that helps the bike find an upright, balanced position.

norsehabanero

most of us have mastered 2 wheels give or take a few skills but how many have tried one wheel
once you have it moving it does balance like a bike (sort of) once you are moving it does get easyer to ride balance wise but it does use different muscles( surpriseing as it seams)
you can train yourself to ride different types and styles if you are willing put yourself through it, the design does help but part of it falls (i think) to the determination of the rider

jcm

You are all 'majoring-in-the-minors' here.
It doesn't matter what the geometry of the bike is, or what the physics of rotational mass are - humans are most definitely hard wired to almost instantly adapt to all types of situations involving motor skills. Not only are we mentally capable of imagining our environment differently, we are also capable of inventing conveyences to make that end. That's the central identifying characteristic in Being Human; the ability and willingness to affect change in the environment. No other species does this.

If you are a strict evolutionist, you might see the ability to balance and control a bike as a left-over from when humans were arborial, having evolved stereoscopic vision and advanced auto-motor control.

If you view us as created beings, a "little lower than the angels" then the abilities are a gift.

Either way, the chimp that went into space in the '60's did nothing apart from being controlled from Houston. A chimp can be taught how to ride a bike, but chances are low that he'll get on one on his own.

For us, it's totally natural.

Maelstrom 

Explain people who can't or have issues riding? How come it doesn't feel natural. There is a progression to all parts of riding. Control, speed, ignoring the mental block of speed, etc...it sure doesn't seem natural to me. Partiall maybe, an innate ability for humans to adapt, but the skill itself is learned.

Using your approach, humans are natural at anything requiring physical aptitude...

cooker

I mostly agree with you: we are adaptable (like many other animals). However, I don't know about "instantly". Gazelles learn to run a lot sooner than we do (like the day they are born). Our balance on a bike is definitely a learned skill and it can take days or weeks to first learn it. It's counterintuitive to countersteer to initiate a turn, and we certainly don't do it in a car or on a tricycle, so it must be learned through trial and error, or taught. Perhaps it's a transfer from our feet where a runner can initiate a turn by stepping to one side to initiate a turn in the other direction, but our hands were not born to do that! Once learned, skills like that can become automatic.

jcm

I said:
"...almost instantly adapt..." Read: observe, learn, try, do.

And:
"For us , it's totally natural." Read: "Yeah Boy Howdie! This is fun!"

Context, gentlemen. Especially important inside this little gray dialog box.

As for some who have issues, well, they either pick up a little slower due to physical differences like equilibrium problems, or, are more fearful - like my very sweet, demure wife. She absolutely refuses to go over 10 mph!

Not all of us are athletically inclined.

rodny71

i agree that the ability to steer the bike is what keeps us upright. on a scooter the wheels are tiny yet it's kept upright because you are steering. when i was teaching my son to ride his bike, he kept falling over, so i told him to steer into the direction that he's falling, like he does on his scooter. he was balancing his bike within 15 minutes.
I also think we can learn to ride a bike alot faster at a young age. I've seen adults try to learn how to ride a bike and its almost impossible.
try riding a bike with the fork locked. no matter how fast you are going you will fall over within a few feet.

cooker

Scooter's gonna fall too.

fordfasterr

I just wanted to throw a wrench into this one...

what about unicycles ?

TYB069

I remember when I took physics, my prof mentioned the experiment with the bike with 4 wheels. He also said that the experiment was flawed. I want to say that it was something about not all the forces cancelling due to relative positions and minor differences in weight and sizes. I can't really remember because I slept through about half the classes but, hey, it was an intro course. About the only thing those classes are good for is naptime.

If you've ever driven a motorcycle/dirtbike/moped, I think you'll realize that gyroscopic forces are definately at work. But yes, alot of riding is simply human balance. I think that in order to ride a bike, you have to figure out how to use your balance to help amplify/counteract (depends) gyroscopic effects.

jur

I really like Sheldon Brown's take: Riding a bicycle is a balancing act that once learned, is never forgotten. (From memory, so may be different in wording.)

TexasGuy

Riding a bike requires absolutley no intelligence and no motor coordination. A dog can ride a bike if you could train it to simply pedal. Cycling involves physics and not intelligence. This last theory is proven time and time again by idiots around the world

DannoXYZ 

Funny you mention that, here's a video of a dog riding a bike

I'm still finishing up some pictures, but the idea is the self-straightening front-end. The trailing contact-patch is pushed backwards by the road to keep the front-wheel aimed straight ahead. The faster you go, the higher your momentum p=mv and the higher the backwards force of the road on the front tyre, forcing it to aim straight ahead. It's like trying to open a car-door while you're moving, the door trails the hinge, and the air forces the door to be straight behind the hinge. Any lateral displacement of the door, or the bike's wheel, gets pushed back inline behind the pivot point. The faster you go, the stronger the self-straightening force. That's why it's harder to turn the bars at higher-speeds than at lower-speeds.

Try it, use just one hand and push forward on one side of the bars at low-speed. One hand is used to isolate the opposing-effect of the other hand. Then at higher-speed, push on that side of the bars again with one hand and notice that the front-end refuses to turn, it wants to go in a straight line.

Albany-12303

I dont think so. This might explain why its its difficult to tip over at high speeds (ie conservation of angular momentum) but the gyroscopic force generated at slow speed with light alloy wheels is very low (one rotation a second does not give much force).

I think that the human ability to make minute corrections in balance is the deciding factor.

Although I concede that the Gyroscopic force on childrens bikes may be high enough to facilitate the maintaining of balance, since the wheels are small (rotate fast) and heavy.

cooker

Or, it could mean that misconceptions are hard to dislodge even among the supposed objective. I can skate on one foot, ski on one waterski, snowboard (badly)...how does angular momentum (ie. gyroscopic forces) help me balance here?

cooker

Dogs have excellent coordination and balance.

cooker

The trail doesn't help you stay upright, except indirectly. The fork is designed so that if you tip the bike, the wheel turns. Thus if you start to fall to one side, the bike turns itself in that direction and rights itself. That's what helps you stay upright, or allows a bike to stay up on its own.

The reason trail helps is that without it, the bike can overcorrect and start to wobble, as seen in that video of the jubilant cyclist letting go of the handlebars and crashing just before the finish line. He had a road bike with minimal trail. A tour bike with large positive trail is more stable, because the trail effect dampens the self-correcting effect, so the bike doesn't wobble out of control.