A bike with a electric motor to provide power but no steering or balancing will not go straight for very long. Yes gyroscopic forces are why a bike is more stable when going faster, but it is the riders ability to balance and manage the various forces acted upon the bicycle that keep it upright.

Gyro effects are only in one plane.....The spinning wheels will only keep the bike stable in whatever plane it happens to be in....until acted on by another force...you or gravity.

If you locked the steering and went fast enough,the bike could hold a 45* angle until it slowed down enough.

If the axle was long enough,you could spin the wheel and hang it from a bench sitting on one side and it won't fall off until it slows down.

I agree but the gyro stability isn't very much at bike wheel speeds. Enough to keep the wheel upright but not a lot more. It's a very small part of keeping the bike up.

You can actually feel how much the force is. Hold the front of a bike up and spin the wheel. Turn the bars while it's spinning. (It will have the same resistance tilting over as to the steering turn) You can feel some resistance, but it doesn't feel like enough to hold a bike up does it?

-with a human on it-
a stopped bike can stay upright
so actual movement of bike parts isn't essential
don't need to build a half assed bike to prove that

The gyroscopic effect has very little to do with how a bike stays upright. As this thread has demonstrated, the real answer is quite complicated, but the answers that deal with steering the bike back and forth underneath you are close.

Standing on one foot is a whole lot harder than walking slowly. The physics of static balance (i.e., don't fall over when you're not moving) vs. the physics of dynamic balance (i.e., don't fall over when you are moving) are totally different. Walkers, skiers, ice skaters, cyclists, etc. are in dynamic balance -- you are constantly moving to a point where you're going to "catch" yourself. You are constantly steering the bike to "catch" your momentary imbalances. If you suddenly "freeze" a walker / skier / ice skater / cyclist / etc. -- they'd fall right over because there's nothing to "catch" them.

As has been said above, it gets easier when you go faster since you have a greater margin for error -- the bike is moving faster to catch you. Gravity (pulling you down) is constant. The speed of the bike is not. It's the same with skiing -- skiing well at a slow speed is extremely difficult, because as you wait, wait, wait, wait for your skis to come around and "catch" the constant imbalances that are created, gravity is pulling you over.

Gyroscopic effect may exist, but it's been proven to not be significant. Mostly it's the geometry of the bike. Above a certain speed, the bike falls further into the turn than it needs to, setting up a fall in the opposite direction. Trail causes the front wheel to lead the way, and the bike wobbles down the road in an upright position. Below that speed, the bike can't fall properly and so just tips over.

The rider has two purposes: to provide power so the bike doesn't slow to below the speed of stability, and to unbalance the bike so it goes somewhere other than straight ahead.

science - how does it work?!?!

The force of the wheels spinning keep the bike upright. The wheels don't want to move side to side, they want to stay upright. (Gyroscopic Force)

The faster you go, the more stiff your steering becomes because of gyroscopic force.

A bicycle will never get going fast enough, under the rider's power, to keep you from being able to steer.

Example 1: You're riding your bike down a steep bridge and you hit 45 MPH...you can still steer...though the handlebars will seem stiff.

Example 2: You're tearing down a drag strip on a top fuel drag bike at 300 MPH...you cannot turn the handlebars to steer...the gyroscopic force of the wheels is so great at this speed that you cannot force the handlebars to turn. (Not that you'd want to at that speed)

Hi,

No. If you force turn the handle bars at speed you will simply fall off, painfully.
The bikes geometry keeps the wheel straight, not the gyroscopic effect.
Its easy to build a completely unrideable bike by making the bikes geometry
inherently unstable. The small gyroscopic effect only stabilises forces a tiny
amount, nowhere near enough to to "damp" any unstable geometry.

Once a bike stops wobbling, and the the faster it goes, the more impossible
it is to ride a straight line and not be balanced, any imbalance will make the
bike turn in an arc. At speed you simply do not steer with the bars, you
steer by balance, your hands stabilising the bars and going with the flow
of your balance. You only have to look where / think you want to move
out and you will with no conscious aware steering input.

Riding a bike a low speeds can involve the steering, and requires some
considerable skill not to fall off. Your balance needs to pre-empt the
effect of our steering input, and the only way to develop that skill
is by lots of practice and probably lots of falling off on the way.

rgds, sreten.

Both your examples are wrong, in reasoning. Its the trail of the
steering geometry that stiffens the steering the faster you go,
as the faster you are moving the more force a given wheel
movement creates by the rate of change of direction.

I painfully found this out as a teen building a boxcart with
poor steering geometry with no straightline stability at all.
(As did a rather large and fat older bully insisting on having
a go, he went fast down the hill and completely totalled.)

Other forum where I posted.

http://www.glocktalk.com/forums/show...hlight=bicycle

Go to the end where the Physics prof explains how he thinks it works.

+1 The OP is asking about the bike with him on it. The inertia of his body provides the greatest of all forces involved.

Humans ride unicycles-can keep them upright- moving or stopped.It would have to be a throughly weird bike to be literally unrideable

Motorcyclist claim-correctly-that you DO move the bars to steer-but in the opposite direction-counter steering-
Counter steering was a LONG debate in motorcycle mags maybe 35 years ago
Just push the right grip forward-you will go right-despite the wheel pointing left.
(At very low speeds different story)

There are one or two good answers in this thread, but I'm astonished at the number of people who obviously haven't got a clue but are having a shot at the answer! It's comical. One chap even seems to believe that gyroscopes don't exist !!

The geometry of the bike helps to keep it upright once it's up to the minimum speed for stability. The purpose of the rider is twofold: provide power and unbalance the bike so it can change directions.

The example of trackstanding actually is good for further illuminating the degree to which the steering is the key. And I'm speaking from experience, because I trackstand a lot.

When the bike is rolling, you correct for a lean by turning the wheel that way. Incidentally, it works the same way on rollers (and the reason the rollers are hard to ride at first is that it's so easy to over-correct). When you trackstand, the front wheel is always turned to one side or the other, and you correct for a lean by riding forward a teeny tiny bit or riding backward a teeny tiny bit. Going backward is essentially the same as if you turned the wheel the other direction for purposes of stability, but it obviously only works if you have very little momentum to change; i.e, if you're stopped. And that is why it's easier to trackstand on a fixed gear, and if you don't have a fixed gear, you can't do it facing downhill. The better you are at it, the finer the corrections you make, and you might be standing just as still as if you were standing on the ground on your two feet, but you're still making them (you're constantly making zillions of tiny corrections, shifting your weight and so on just to stand still on two feet, too).

Trackstanding with no hands is possible too, because the bars will generally fall into the right amount of turn to compensate for how your weight is balanced. The same is true for riding with no hands. In reality, you do not steer a bicycle by turning the handlebars, you steer by shifting your weight and compensating for the lean you have caused. Your hands are just on the bars to stabilize them so they don't hit a bump and suddenly do something unpredictable (there are some small exceptions to this in the case of quick swerves around obstacles where you swerve the bike out and then back under you again, etc). If you over-tighten your headset, it becomes very difficult to trackstand or even ride with no hands. Tighten it more and it becomes difficult to steer even with your hands on the bars. Bolt the front wheel in place and even if you're a really good rider, you'll have a very hard time going very far without falling because you will not be able to correct for the slightest shift in your weight.

So, did you buy and read the book I recommended in post number 5.. it is the definitive work

of a PhD at MIT ( and his grad students) who studied the Physics and engineering .. of just that.

The theory that gyroscopic principle kept a bike upright was thoroughly discredited years ago.

If you think about it, the gyroscopic theory is fairly easy to debunk yourself. Hold a wheel in your hands by its axle and spin it. Tilt it from side to side while it's spinning. You do feel a certain amount of resistance to tilting it, but not all that and you can still tip it pretty easily, even if it's spinning fairly fast. Even if you were holding two wheels, it wouldn't be that hard. Now put someone about your size on a bike standing still, and try to keep them from falling over while only holding onto the rear axle with your fingers exactly the way you did with just the wheel. If the gyroscopic motion of the wheel were enough to keep the bike upright with a rider on it, it would be easier to hold the bike up than it would be to tilt two wheels.

My guess is that you do not need to actually try the above experiment.

I've ridden a bike with four wheels, the top two either turn in the opposite direction to have zero net angular momentum or sit still.

The difference in riding the bike in the two modes was very small. As has been repeatedly started, angular momentum plays a quite small in bike stability.

Ski bikes! No gyros! http://www.lenzsport.com/skibike_main.php

Newton-
"equal and opposite reaction" you pushed yourself over
And KARMA of course