What exactly causes a bicycle to stand upright?

[Chap]

There seems to be some controversy around this topic. I initially thought that it's the gyroscopic effects keeping it upright ( which was supported by the fact that a bicycle may roll downhill by its own), but then I met the argument that those effects are not very strong.

 

I agree with this argument because I think the gyroscopic effects felt by the bicycle is sufficient enough to support a riderless bicycle, but not one with a rider. I mean, a bicycle just weighs a few kilograms, but I weigh 60kg! So the effect it not powerful enough to support me. Am I correct?

 

I came across another theory that; "our brains learn to keep the bicycles upright by making necessary adjustments unconsciously to balance the bicycle." I partially disagree with this theory since I don't believe that our brains are responsible for the whole balancing act without any help. If this theory is true, I should be able to keep a non-moving bicycle upright. I can't balance a non-moving bicycle for more than a few seconds (no matter how much time I spent practicing) , but I can ride for hours on a moving bicycle.

 

I'm sure something else is involved, but can't exactly find it. I would like to know your views. Please state it in simple terms; I'm a biochemistry undergraduate; physics is not my area of expertise.

 

Thanks.

[ydoaPs]

From what I gather, no one really knows aside from the rider balancing. There have been bikes built that cancel the gyro effect and they still work. Some people thought it was because the front wheel moves, so it's hardly ever in a true straight line with the back. Then they made a bake with a stationary front wheel that still worked.

[J.C.MacSwell]

The rolling motion of a wheel, on a surface that allows traction, is self stabilizing. It will naturally turn toward the side it might lean, which will tend to straighten it up. This is not just a gyroscopic effect. Compare a wheel on ice or very slippery surface which will much more easily fall over.

 

Steering can add (or subtract) from this effect and of course a non-moving bicycle essentially has no steerage. (there are techniques for staying upright, but it is much more difficult)

Edited April 29, 2012 by J.C.MacSwell

[StringJunky]

It seems to be a combination of several effects that contribute to upright-stability:

 

A bike remains upright when it is steered so that the ground reaction forces exactly balance all the other internal and external forces it experiences, such as gravitational if leaning, inertial or centrifugal if in a turn, gyroscopic if being steered, and aerodynamic if in a crosswind.[15] Steering may be supplied by a rider or, under certain circumstances, by the bike itself. This self-stability is generated by a combination of several effects that depend on the geometry, mass distribution, and forward speed of the bike. Tires, suspension, steering damping, and frame flex can also influence it, especially in motorcycles.

 

http://en.wikipedia.org/wiki/Bicycle_and_motorcycle_dynamics

 

The above link is worth a read.

Edited April 29, 2012 by StringJunky

[granpa]

I saw this and thought of this thread

 

[Cabwood]

I reckon that a bicycle stays upright while in motion because if it leans to one side, the front wheel falls to the same side (probably due to gravity, and maybe due to the front wheel's fork being forward of the steering pivot). That causes the wheel to pivot to that side, and the bicycle turns in the direction it is falling, countering the fall. It is inherent negative feedback.

 

A test for this would be to fix the steering in the straight position and see if it falls over when pushed off at speed. Another experiment would be to modify the bike so that the fork points backwards and see how that affects the stability.

[JohnStu]

there are many ways to explain it, I put the forces into these two:

 

- the fast-enough spinning causes the center of its mass to remain very close to the center

- the constant change of ground surface does not give enough time for it to tip to one side

[Ronald Hyde]

This is a fun topic. If you notice, the bicycle is designed so that if it tends to fall to one side the front wheel turns in such a way as to 'correct'

the falling motion. I doubt anyone thought of this, they just tried different things and this worked. That and angular momentum.

[John Cuthber]

In my experience as a kid, the combination of me and the bike stayed upright fairly well

I stayed upright without the bike.

The bike without me fell over (even if it was moving)

I conclude (with no great surprise) that the answer to the question "What exactly causes a bicycle to stand upright?" is

 

The Rider.

[Bill Angel]

There is an interesting article and video about a robot riding a bicycle:

http://www.geek.com/articles/geek-cetera/amazing-little-robot-manages-to-ride-bike-unaided-20111025/

 

Watching the robot ride the bike in the video, one notices that it's his jerky arm movements on the handlebars that keep the bike upright. The robot can't lean to one side or the other to affect the stability of the bike.

[Amaton]

In my experience as a kid, the combination of me and the bike stayed upright fairly well

I stayed upright without the bike.

The bike without me fell over (even if it was moving)

I conclude (with no great surprise) that the answer to the question "What exactly causes a bicycle to stand upright?" is

 

The Rider.

 

Ever tried riding with your hands to your sides? Good for about 2 seconds until you feel the bike start to shift and reflexively grab the handles again. The bike would've fallen if you had not acted so quickly, but thankfully you did and it did not fall. So I agree that it's simply the rider conducting its movement.

[John Cuthber]

Ever tried riding with your hands to your sides? Good for about 2 seconds until you feel the bike start to shift and reflexively grab the handles again. The bike would've fallen if you had not acted so quickly, but thankfully you did and it did not fall. So I agree that it's simply the rider conducting its movement.

You need to learn to ride properly.

 

http://www.youtube.com/watch?v=ZvrRRwJVrSA

Edited September 26, 2012 by John Cuthber