Most people don't know how bicycles actually work.
- [Off screen] Let's try it again.
So we modified this bike to prove it.
This video was sponsored by KiwiCo.
More about them at the end of the show.
- When you're riding a bike and you want to turn left,
I think most people just imagine
you turn the handlebars to the left.
This is a bike to test whether that is true.
And it's made by my friend Rick here.
and he's got a radio controller that allows him
to lock out the steering to one side.
So, what he's gonna do is as I'm biking,
he's gonna pick whether I can turn
either to the left or to the right.
So, go for it.
- [Rick] I'm giving it a left turn.
It pulls the pin out,
but you can see that you can still fully steer
after I've pulled the pin out.
I've armed it.
There's where it locks. - OK
Now, that that's when your LED comes on
and that just says turn that way.
- Turn left. - Yeah
And if I try to turn right, I can't.
And if I try to turn left-
- You can.
- I can.
So the question is
can I successfully execute this left-hand turn?
Should we give it a shot?
I mean, he's not gonna tell me whether it's left or right,
so I have to look at the LED to know
which way I can still turn.
- [Rick] You let me know when you're ready.
- Okay.
(exclaims)
No!
That was meant to be a turn to the right
but there was no chance in hell.
Left.
(exclaims)
Right.
All right.
(exclaims)
Right, right, right!
God!
- If you look closely, you can see the problem.
Here, I'm trying to turn right
but steering that way puts me off balance.
If you could ride this bicycle,
you would find it's impossible to turn left
without first steering right
and it's impossible to turn right
without first steering left.
This seems wrong.
I think most people believe you turn a bike
simply by pointing the handlebars
in the direction you want to go.
After all, this is how you drive a car.
Point the front wheels any direction you like
and the car just goes that way.
But the difference with a bicycle
is steering doesn't just affect the direction you're headed;
it also affects your balance.
Imagine you want to make a right turn
so you steer the handlebars to the right.
What you've done is effectively
steered the bike out from under you.
So now you're leaning to the left
and the ground puts a force on the bike to the left
so the only way not to fall
is to steer the bike to the left.
You have made a left turn.
If you really wanted to turn right,
you first have to counter-steer to the left
so you can lean right into the turn.
This is something anyone who rides a bike knows intuitively
but not explicitly.
- Turn left!
- Film someone riding a bike towards you
and tell them which direction to turn
and you will find that they counter-steer
without even thinking about it.
- Hard left!
When you're riding a bike,
it's exactly the same as what we call an inverted pendulum
or balancing a broomstick on your hand.
If I'm balancing it and I just start walking toward you,
it will always fall away from you.
If I want to walk towards you, it's easy enough to do
and people inherently know how to do it.
If I pull it backward, I can now start walking that way.
I have to initiate the lean to turn into it.
- If you want to move the pendulum somewhere,
you first move the base in the opposite direction.
And now the pendulum is leaning
in the direction you want to go
so you can move with it.
And it's the same with a unicycle.
In order to go forward,
first, you have to peddle back.
So, you're leaning forward
and then you can go forward with it.
- Everything you're doing on a unicycle
is all about keeping that contact patch
right where it needs to be relative to you.
You're balancing the broomstick.
It's just that on a unicycle,
you do the longitudinal balance with the pedals
and you do the lateral balance, the side to side,
the same as you do with a bike.
You essentially- sorta, small counter-steer to get that weight,
to get the contact patch out,
and then you can pedal and bring it under you.
- Now I should point out
that sometimes when the steering locked,
we just happened to be leaning in the right direction
to execute the turn.
- Right, right, right, right, right!
Right, right, right, right.
- [Off Screen] Oh, managed it!
- Essentially by sheer luck,
we had counter-steered
before that side of the handlebars locked out.
Now, I can keep going.
- [Rick] Yeah, but don't turn left
or you're gonna be screwed.
- I can't turn left.
What's interesting about this is it shows
that you can still ride the bike perfectly well, right?
It's just you can't turn left.
The funny thing is that you couldn't initiate the turn.
I mean, the wild takeaway is that
steering is not just for turning the bike;
steering is for balancing.
- That's exactly right.
- Why is it hard to balance on a stationary bike?
I think most people believe
it's because the wheels aren't spinning
so there's no gyroscopic effect,
but that's not it.
The truth is you use steering
to keep the bike underneath you
but steering doesn't work when you're stationary.
Your balance comes not so much
from how you position your body over the bike,
but by how you steer the bike to keep it underneath you.
Even when going straight,
you're constantly making small steering adjustments
to maintain balance.
- You're moving the contact patch
of the front wheel under you.
You're doing exactly what you do
when you balance a broomstick on your hand.
- So, if the rider is responsible
for steering the bike to keep it balanced,
how do bikes without riders stay upright?
As long as a bike is moving with sufficient speed,
it can keep coasting indefinitely.
I first became aware of this phenomenon
through the great videos by MinutePhysics,
which inspired me to make this video.
You should definitely check them out.
But it turned out the ground
where we went to test this effect was really bumpy,
but the bike still manages to absorb all these perturbations
and remain stable.
So, how does it do this?
I think most people believe it's the wheels spinning
that creates some sort of gyroscopic effect
that resists falling over
just like in this demonstration of gyroscopic precession.
Yhe wheel stays upright
even though gravity is pulling it down.
But this is not why bikes are stable.
Just watch what happens
when we lock the handlebars completely
so you can only go straight ahead.
- Locked out, locked out.
Whoa!
- All that is happening is the steering is locked.
You just got to ride it.
You don't have to turn.
You just ride.
Letting go.
- Some people tried going really fast.
(group laughs)
Others experimented with extreme balancing techniques.
- He's leaning. Don't go too fast!
(group laughs)
- But even with the gyroscopic
effect of the wheels,
no one was able to keep the bike upright
for more than a few seconds.
(crowd exclaims)
- This is not safe for a second.
- It is just as hard to balance
on a bike with locked steering
as it is to balance on a stationary bike.
- No, this one is impossible.
- Because you can't steer the bike
back under you.
The real reason bicycles are stable without riders
is because they're cleverly designed to steer themselves.
If they start falling to one side,
the handlebars turn in that direction
to steer the wheels back underneath them.
At least three mechanisms
are responsible for a bike's corrective steering.
The first is that due to the angle of the front fork,
the steering axis intersects the ground
in front of where the wheel touches the ground.
So, if the bike starts leaning to the left,
the force from the ground on the tire
turns the wheel to the left.
If the bike starts leaning right,
the force from the ground pushes the wheel to the right.
The front wheel of a bicycle is essentially a caster wheel,
like those you find on strollers or shopping carts.
Whichever way you drive them,
the wheel falls in line and rolls in the same direction.
The second reason for a bike's corrective steering
is that the center of mass
of the handlebars and front wheel
are located slightly in front of the steering axis.
So, when the bike leans left,
their weight pushes the front wheel to the left.
If the bike leans right, their weight steers to the right.
And the third mechanism is a gyroscopic effect
but it doesn't keep the bike upright directly;
it just helps steer.
If you have a gyroscope
and you push down on the left-hand side,
the gyro will turn left.
If you push down on the right side, it will turn right.
This is known as gyroscopic precession.
It seems as though the force you apply
takes effect 90 degrees from where you applied it.
So, bikes are stable primarily because of steering.
They have built-in mechanisms for steering themselves.
In fact, you don't need all three mechanisms
to create a stable bike.
Researchers created this weird-looking bicycle
to prove a point.
It has no gyroscopic effect
thanks to counter-rotating wheels
above the wheels that touch the floor.
Plus, there is no caster effect
because the front wheel touches the floor
in front of the steering axis.
But this bike is made stable by its mass distribution,
the force of gravity on which
steers it in the direction of any lean.
Understanding how bicycles work
is still an active area of research.
There is a program you can use to input
all the different bicycle parameters
and see the range of speeds over which it is self-stable.
And this research is leading to better bikes.
This prototype has a smart motor in the handlebars
to actively help steer,
keeping the bike upright even at low speeds.
I guess it's fitting that we are still
learning new things about bicycles
since most of us are able to ride one
without any knowledge of how we're actually doing it.
(futuristic sound effects play)
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