What keeps a bicycle upright?

While moving of course.

Originally posted by Metal Brain
While moving of course.

The balance of the person riding plus the spinning wheels give gyroscopic effect which helps to keep it upright also. Faster=more vertical stability.

Originally posted by sonhouse
The balance of the person riding plus the spinning wheels give gyroscopic effect which helps to keep it upright also. Faster=more vertical stability.

Why, when I was a kid and tried to ride a bicycle 'hands free,' would I always veer off to the left? (Same thing happened when I hit a golf ball or kick a football).

This has troubled me all my life...

Originally posted by Ghost of a Duke
Why, when I was a kid and tried to ride a bicycle 'hands free,' would I always veer off to the left? (Same thing happened when I hit a golf ball or kick a football).

This has troubled me all my life...

If you are right leading then the right hand side of your body is a little stronger. This means that when you push with what feels like equal strength with each arm or leg you'll tend to get a torque, because you're not actually using equal force. Although on a bicycle I'd have expected that to cause you to veer to the right. Are you left handed?

Originally posted by Metal Brain
While moving of course.

Magic.

Originally posted by DeepThought
If you are right leading then the right hand side of your body is a little stronger. This means that when you push with what feels like equal strength with each arm or leg you'll tend to get a torque, because you're not actually using equal force. Although on a bicycle I'd have expected that to cause you to veer to the right. Are you left handed?

Alternatively the bicycle's wheels and/or frame could have been misaligned, which is not uncommon.

Originally posted by Soothfast
Alternatively the bicycle's wheels and/or frame could have been misaligned, which is not uncommon.

That wouldn't explain the symptoms spreading to golf and football.

Originally posted by DeepThought
If you are right leading then the right hand side of your body is a little stronger. This means that when you push with what feels like equal strength with each arm or leg you'll tend to get a torque, because you're not actually using equal force. Although on a bicycle I'd have expected that to cause you to veer to the right. Are you left handed?

Yes left handed (and footed). When I kicked a football friends always called it a banana kick. 😞

Originally posted by Ghost of a Duke
Why, when I was a kid and tried to ride a bicycle 'hands free,' would I always veer off to the left? (Same thing happened when I hit a golf ball or kick a football).

This has troubled me all my life...

Wheel alignment.
The front fork of a bicycle is designed to automatically cause it to steer forwards. However, if the axils are not correctly centred then the bike will tend to preferentially steer to one side. The result is you have to lean the other way to go straight (hands free).
Bikes with a more vertical steering column are noticeably harder to ride hands free.
As for golf and football - that's on you.

Originally posted by Metal Brain
While moving of course.

If a bicycle is falling to one side, and you steer to that side, the momentum of the bicycle is now slightly in the opposite direction which rights the bicycle. So the secret to riding a bike is to steer towards the direction you are falling. The design of the steering column helps by causing the bicycle to automatically steer in the direction it is falling or stay directly straight when upright. (assuming the wheels are correctly aligned.)

Originally posted by sonhouse
Faster=more vertical stability.

Is there a point where the stability decreases the faster you go? For example, is a bike moving at 100 km per hour more stable than a bike moving at 30? Is a bike moving at the speed of sound more stable than a bike moving 100 km per hour?

Originally posted by Ghost of a Duke
Why, when I was a kid and tried to ride a bicycle 'hands free,' would I always veer off to the left? (Same thing happened when I hit a golf ball or kick a football).

This has troubled me all my life...

You really have nothing to offer in regards to science.

Originally posted by vivify
Is there a point where the stability decreases the faster you go? For example, is a bike moving at 100 km per hour more stable than a bike moving at 30? Is a bike moving at the speed of sound more stable than a bike moving 100 km per hour?

It depends on your wheel balancing and the smoothness of the road.

Originally posted by sonhouse
The balance of the person riding plus the spinning wheels give gyroscopic effect which helps to keep it upright also. Faster=more vertical stability.

There is no significant evidence that the gyroscopic effect plays any part.

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

http://socrates.berkeley.edu/~fajans/Teaching/MoreBikeFiles/JonesBikeBW.pdf

In the PDF, a bicycle was created with an extra counter rotating wheel to counter gyroscopic effects. It was still rideable. Although it did make the bicycle fall over faster if it was not being ridden.