Question

How to steer a bicycle ?
Please explain how to bring the cycle back to its initial position (no tilt) ? Do we have to counter-steer again ?

See : http://socrates.berkeley.edu/~fajans/Teaching/Steering.htm

Answer 1

No tilt meaning?! You cannot turn without tilting.. counter steering is always there, although you don't notice it..
and when you are towards the end of the turn, you automatically stop leaning, so inertia pushes u back!

Answer 2

Counter steer again?!?

yes yes.. correct!

Answer 3

By "No tilt" I mean the position in which we are NOT leaning (and traveling in straight line)

While turning we are in equilibrium (w.r.t. C.O.M.). One way to get back straight is to increase the velocity and the centrifugal force will unbalance the equilibrium and push us outwards.

But it is risky to accelerate while turning (we may slip too). Hence, I wanted to know - "can we use the steering to get back straight up" ??

Answer 4

BTW, don't you think counter steering might lean us even more..and we might end up kissing the ground.. XD

Answer 5

Counter steer in the other direction :P

Answer 6

come to think of it.. i have never actually thought about how we get back up :D..

if you take a tire.. u see, it ll keep turning once started, until it falls on the ground

Answer 7

right?

Answer 8

I have seen a (single) tire moving in a curly fashion (when it has a good speed).
Although it might be due to uneven-ness of the road..

Answer 9

@Vincent-Lyon.Fr
@douglaswinslowcooper
@agent0smith
@ybarrap

Answer 10

Angular momentum (of the wheels) helps you to get back to an upright position.

Answer 11

After (b) ; the conservation of angular momentum causes the whole system to have a angular velocity in downward direction. The steering will have an additional angular velocity in downward direction (turning it from left to right).

So you mean to say that, position (d) is the state of equilibrium for the turn (w.r.t C.O.M.) & position (e) is when the bicycle starts getting back up ??

Answer 12

Conservation of angular momentum is essentially what keeps a bicycle upright. Once the wheels are spinning, they want to maintain that angular momentum.

Changing it (like by tilting) doesn't stop them from wanting to maintain that angular momentum (which was initially in an upright position).

Answer 13

And inertia carries you back to an upright position, too.

Answer 14

I know the article is implicitly talking in terms of conservation of angular momentum. I can't understand whether (d) or (e) is the stable position for moving on a circle.

Also, while on a turn; the torque due to centrifugal force balances the torque due to gravity. Hence, unless we increase the velocity (quite risky) or change the angle of inclination; we can't get back up.

Answer 15

Oh, I forgot to mention..I calculated torque from the point of contact of bicycle and ground.

Answer 16

I can't really tell what d and e are showing with those pics.

But it's inertia that is trying to make you go upright again, not centrifugal force.

Answer 17

By 'inertia' I thought you meant 'inertial force' which (I guess) refers to pseudo force..
IDK what do you mean by "it's inertia that is trying to make you go upright again"

Answer 18

I try to avoid calling it inertial force - inertia isn't a force. Your inertia is still trying to carry you in a straight line (tangential to your current circle of motion)

But to "get back up" you'd just straighten out the front wheel, then inertia will carry you upright, since the front wheel is the only thing keeping you turning.

Answer 19

Inertia and angular momentum of the wheels will straighten out the bike. Inertia wants you to go in a straight line, tangent to the circle.

Answer 20

Well have you seen that batmobile bike in darknight ?
It doesn't have a steering (meaning you can't turn the handle).. it only works on your weight.. you can actually steer into a nice circular motion just by tilting,, so i say, your position d should be enough .. the reason i think normal two wheelers do have steering is so that we can take turns even when we are moving slowly..
you may notice while overtaking and all, the steering hardly gets turned, its only the tilting that matters.!

Answer 21

when you tilt, you torque.. so you stop tilting , you stop torquing and you come right back up!

Answer 22

But we can't tilt without steering..I yet have to see batmobile in real life :(

Answer 23

You can.. are you telling me you can't shift your weight (off center it?)

Answer 24

Hmm... I don't think a bicycle can turn without the front wheel turning (it'll tilt/turn as a consequence of you tilting).

Answer 25

I can shift my weight off-centre..but if I somehow the bike tilts while the front wheel is in straight alignment..conservation of angular momentum would be 'violated'..

Answer 26

@agent0smith
"But to "get back up" you'd just straighten out the front wheel,.."

If the front wheel is in straight alignment, the angular momentum would be perfectly conserved. See the attachment.

Answer 27

Hence, conservation of angular momentum wont force the bicycle to get back up..

Answer 28

But your inertia will.

If the front wheel was locked, and you leaned far enough, I think you'd just fall over if you leaned too far. Just like you fall over if you're moving too slowly - the conservation of angular momentum only keeps the bike upright if you're moving fast enough (because the wheels have more angular momentum).

Answer 29

I don't see how inertia will act on demand..I mean while taking the turn, friction force (cornering force) provides the necessary centripetal acceleration..so it would be like a simple circular motion..I don't see how all of a sudden, the circular motion changes into to rectilinear motion..

Answer 30

Inertia is wanting you to go in a straight line at every point during a turn. You keep turning as long as the front wheel is slightly turned.

Answer 31

Ok so if you guys say that when the front wheel is aligned with the back wheel, its impossible that the vehicle would turn, (maybe if you lean, the vehicle tries to turn as a whole, and friction counters it) in that case, you know that in order to continuously keep turning into a radius, your front wheel needs to be turned a little so position (e) and not position (d)

Answer 32

Inertia always acts, just that you provide a force to counter it. It doesn't decide to act - you just notice it more when you stop providing a force to counter inertia.

Answer 33

And so when you are IN that turned position.. your inertia is always trying to pull you away from center.. so you just stop torquing (tilting) and let the inertia do its thing, and you ll come right back up, (this also conserves the angular momentum)

Answer 34

Btw - circular motion frequently turns into tangential motion - as soon as the force providing centripetal force disappears. Swing an object in a circle, on a string - if the string breaks, the object will move tangentially due to its inertia.

Answer 35

"..maybe if you lean, the vehicle tries to turn as a whole, and friction counters it.."
That's true..but how do we lean in the first place ??..& there comes the role of steering..

"..you just notice it more when you stop providing a force to counter inertia."
That's my question..How do we stop providing the force that counter inertia..note that the concerned force is an external force..

Answer 36

^ you stop tilting the front wheel.

A bicycle only turns if the front wheel is turned and you're leaning.

Answer 37

"but how do we lean in the first place ??"
Its easy.. shift your weight off center :P.. you don't really need steering to tilt you know..

"note that the concerned force is an external force.." be careful here, if you consider the bike and the rider together as your system, the the force that you provide while tilting hence creating a torque WILL BE AN INTERNAL FORCE, and THEREFORE THE MOMENTUM OF THE BIKE AND YOU AS WHOLE IS CONSERVED..
but if you only think of the bike as your system, then you are right that your torque is external, and so you the angular momentum of the bike obviously changes (cause it tilts)

Answer 38

As I showed in the attachment..If we keep the front wheel in straight alignment, the angular momentum will remain conserved. Hence, all the forces that were acting so far will continue to exist.

In other words, as angular momentum is already conserved. Now if the bicycle starts turning back up, there would be an additional angular momentum (which requires a torque).

Answer 39

ok i think.. what i said is absolute B.S

you tilt cause when you put your weight off centre.. GRAVITY puts a torque.. so when you consider bike and the rider as your system, there is a net external torque.. and so the angular momentum of the system Will change. !

but if you consider, only steering the front wheel, in which case you don't really need any gravity, in that case ALSo the bike tilts to CONSERVE the angular momentum

the net result in either case i think is the same?!

Answer 40

In your attachment, the front wheel is not aligned.. they haven't shown the front part.. i don't think the front wheel is aligned.. else how does it tilt?

Answer 41

there is a green omega upwards.. from where do you get that? that is due to steering the front wheel towards the left

Answer 42

"you tilt cause when you put your weight off centre.. GRAVITY puts a torque"
If the rider shifts his weight on the left, the C.O.M of bike would shift towards the right

(as the C.O.M. of the system cannot undergo any lateral displacement due to internal interactions)

Hence, the net torque due to gravity would turn out to be 'zero'.

The attachment show the case when the bicycle is already tilted at an angle and the front wheel is aligned with the back wheel. It is (nearly) equivalent to position (d)

The green omega upwards denotes the angular momentum of the whole system (as it is moving on a circle).

Answer 43

The red omega shows the angular momentum due to rotation of wheels.

Answer 44

Instead of omega, I should have used A..as the angular momentum remains conserved, not the angular velocity..But I find it easier to think in terms of omega.. also A denotes Ampere XD

Answer 45

"If the rider shifts his weight on the left, the C.O.M of bike would shift towards the right " this is only true if you are in vacuum with no other forces

if C.O.M cannot change, then when you are standing still, why do you fall? :P.. (you can once perfectly align the C.O.M such that the Normal force and mg are aligned to give torque zero .. unstable equilibrium) and then you would be able to balance just like that,, even if you moved or danced around right?
but the fact that there are external forces makes sure COM shifts!

Answer 46

So I still stronglyyy believe, that gravity plays a role in tilting and torquing (without the actual need for steering to do it), and then like you guys said, the steering is needed, otherwise, the bicycle may not turn.. and then when u come out of the corner, you just shift your weight back , and u come back up all nice and dandy :D..

Answer 47

By external forces, due imply Brownian motion ?? o.O

BTW, on a perfectly frictionless surface, we can stand still (unstable equilibrium) but any attempt to move will require friction.

Answer 48

*do you

Answer 49

I think steering towards the direction of inclination might help us to get back up (like if we are inclined towards left, we need to steer the front wheel towards left)..but it will call for a real faith in physics to do such a daredevil act XD

Answer 50

I wonder how can we ride a bicycle just by instincts..

Answer 51

"I wonder how can we ride a bicycle just by instincts.." cause we are part of nature, and so our body immediately adjusts to nature, its only the thinking part that is tough.. its true for all animals

anyhoo,"BTW, on a perfectly frictionless surface, we can stand still (unstable equilibrium) but any attempt to move will require friction." so even if i danced around on the bicycle i wouldn't fall? :D.. its hard to conceive.. isn't it.. but I think you are right about that.. that's more or less the reason why we can't just take a flip in mid air.. but then again, in mid air, you don't have normal force acting on you!

Answer 52

if you see the motion of the cycle in the cyling race or something. its exactly like you say.. the cycle shifts opposite to the rider and maintaining the position of COM, but since there IS friction, i think that helps us to off center it.. and thus allow gravity to torque us!

Answer 53

It's hard to understand this concept by looking at a cycle race, things happen too fast & the role of steering is very subtle..

BTW, friction WONT act in lateral direction unless there is a tendency to slip laterally.

Answer 54

I took cycle race to depict your point of COM not shifting when you shift your weight

if friction doesn't do it, what makes you fall from that unstable equilibrium? :P..

Answer 55

air? :D

Answer 56

How does a take a turn then? it has to be due to gravity right?

Answer 57

tyre*

Answer 58

"what makes you fall from that unstable equilibrium?"
1) The tendency to slip exceeds the maximum possible static friction.
2) The angle of inclination is greater than what's necessary (as it is an unstable equilibrium)

The tendency to slip can only be attributed to conservation of angular momentum.

The same reasoning is also applicable to turning of a (single) tire. Although, the inclination in that case arises due to lack of symmetry.

Answer 59

No i am talking about when you are rest. You know what this is going no where.. I ll wait for someone else to shed some light on this :P

Answer 60

then we can talk about gyro's maybe.. XD

Answer 61

And how a cat takes a flip in mid air XD XD..

Answer 62

Er..we are already talking about the concept of gyroscopic precession here..

Answer 63

Yea but gyro's are more BadAss!

Answer 64

Maybe you're right, we should wait for another pair of eyes.. B)

Answer 65

http://hyperphysics.phy-astr.gsu.edu/hbase/mechanics/bicycle.html

Answer 66

Ah haa... what i have been trying to tell you :P.

Answer 67

Agent smith whats up? caught Mr. Anderson yet? :P

"BTW, friction WONT act in lateral direction unless there is a tendency to slip laterally". Friction does act .. when i lean, i push against the bicycle.. the bicycle doesn't move laterally because of the friction! tada!!! :D

Answer 68

Haha i kinda left a while ago, but kept reading this, might add to it tomorrow