[dools]

You can measure it for yourself: balance on the bike when it is stationary, then compare the experience to when you're moving.

When you are moving, it adds in the gyroscopic balancing effect.

Gyroscopic motion means that the force applied acts about 90 degrees later, so when you turn the handlebars which are on a (roughly) vertical axis (call it the "z" axis), the force of that turn is actually applied about the axis that runs from front to back (call it the "y" axis). Gyroscopes "translate" the force.

If you're stationary, and there is no gyroscopic motion, then the only thing that turning the wheel really does is allow you to move the front of the bike to the left or right in order to change your centre of gravity.

[mr_mitm]

My professor debunked this in experimental physics 101. He installed counter wheels on the wheels which spun in the opposite direction (without touching the floor obviously) and was able to still ride the bike just fine.

It may play a part in the effect, but does not explain it entirely.

[dools]

Well, you can debunk that debunking easily enough if you have a bike.

Stand in front of the bike and lift up the front wheel, holding one fork in each hand.

Attempt to turn the front wheel from side to side without the seat changing position at all.

Now hold the bike up with one hand and with your other hand spin the front wheel as fast as you can.

Now with the front wheel still spinning, go back to holding one fork in each hand and attempt to turn the front wheel side to side without the seat moving at all. You will find it more challenging to do and you will notice that the tendency is for the seat to move in the opposite direction from that which you turn the front wheel.

That is, you turn the front wheel towards your right side, the seat will move towards your left side.

This is the "counter steering" effect that we use in order to balance when riding a bike, and it's entirely due to gyroscopic motion.

[Someone]

I don’t see how that debunks that debunking. That professor didn’t claim there is no gyroscopic effect, but that it isn’t necessary to ride a bicycle.

> This is the "counter steering" effect that we use in order to balance when riding a bike, and it's entirely due to gyroscopic motion.

If that’s true, gyroscopic motion is necessary to ride a bicycle.

See also http://www3.eng.cam.ac.uk/~hemh1/gyrobike.htm (with a few good links at the bottom for those who need more convincing), which says:

“It is almost certain that gyro effects are important at the initial stage of steering manoeuvres. […] My point is that gyroscopic effects are not needed to keep you from falling over when you are riding in a straight line. I am not saying anything about what happens when you actively wish to steer away from straight ahead.”

It also does some calculations that show how small the gyroscopic force is compared to the weight of (bicycle plus rider)

So the gyroscopic effect isn’t necessary to balance a bike, but likely helps in making turns.

[david-gpu]

The gyroscopic effect is not necessary, and it has been demonstrated both in reality and in simulation [0].

The central principle behind why a bicycle is self balancing while in motion is the fact that it self-steers in the same direction that it is leaning, which counteracts the fall [0][1].

[0] https://en.m.wikipedia.org/wiki/Two-mass-skate_bicycle

[1] https://m.youtube.com/watch?v=9cNmUNHSBac

[pawplo]

Gyroscopic effect is not needed at all and this is a proof: https://youtu.be/Y5b0DKfhPc4?t=356

[pubby]

Nah, that's not it. Try riding a bike in reverse (or pushing it). It's not at all stable, because the feedback is applied in the opposite direction. You'll fall right away, even though the gyroscopic effect is identical.

[dools]

That's no different from inverting your mouse direction in Quake, you just have to get used to it.

[pubby]

I'd recommend just googling how a bike works instead of pursuing this argument. There's lots of good articles, like this one: http://www.cyclelicio.us/2011/bicycle-dynamics/ It looks like my theory on wheel angle may not be entirely true either. You can also find videos on youtube.

[dools]

The Veritasium video is the best one I've seen but he only describes how counter steering works at slow speeds which is more like how you balance a stationary bike. The faster you go, and the bigger the wheel, the more the counter steering is done by gyroscopic motion than moving the wheel back and forth beneath you.

[Lio]

You could disprove that by letting a bike, without rider, roll down a slope.

If it rolls oriented forwards it will stay upright by itself because of the steering.

If it rolls oriented backwards it falls over because the steering now pushes it off balance.

If the gyroscopic force was the most important thing keeping it upright it wouldn't matter which orientation you let it roll.