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Author Topic: Why does leaning a motorcycle make it turn around a corner?  (Read 41678 times)

Offline chris

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Why does leaning on a motorbike cause it to turn? And is it true that counter-steering - turning the handlebars in the opposite direction to the turn - can actually make you steer around the corner better?

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Offline lightarrow

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Why does leaning a motorcycle make it turn around a corner?
« Reply #1 on: 28/05/2009 23:33:53 »
Why does leaning on a motorbike cause it to turn? And is it true that counter-steering - turning the handlebars in the opposite direction to the turn - can actually make you steer around the corner better?

Chris
Not "better", it makes it possible to steer.
Leaning is either a consequence of counter-steering and a way to reduce the effect of centrifugal force.
 

Offline LeeE

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Why does leaning a motorcycle make it turn around a corner?
« Reply #2 on: 29/05/2009 17:05:27 »
Just leaning a bike over doesn't make it turn, not unless there's something badly wrong with its frame geometry.  The bike will only change direction if you move the handlebars, and you then need to lean the bike to keep the CoG over the path.  At low speeds the degree of lean is unnoticeable but at higher speeds the amount of lean required is obvious.

You only need opposite steering when you're in a state of 'over-steer'  this is when the rear of the bike, or car, has lost grip and is sliding towards the outside of the curve.  The axis of the vehicle is thus pointing inside the curve instead of around it, hence the term 'over-steer'.  Opposite steering is then needed to stop the vehicle from pivoting around its front wheel(s) and spinning.

Although over-steer looks good and can be fun, it's not the fastest or most efficient way to corner because you can only do it once you have lost grip.
 

Offline lightarrow

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Why does leaning a motorcycle make it turn around a corner?
« Reply #3 on: 29/05/2009 23:30:49 »
You only need opposite steering when you're in a state of 'over-steer'  this is when the rear of the bike, or car, has lost grip and is sliding towards the outside of the curve. 
You need opposite/counter steering every time you have to make a bend, not only when you drive as a speedway bike...
If you don't believe me, take a bike, go at normal speed (not too low) and then steer, a little, towards left. Than tell me which way the bike goes.
« Last Edit: 30/05/2009 12:30:37 by lightarrow »
 

Offline LeeE

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Why does leaning a motorcycle make it turn around a corner?
« Reply #4 on: 30/05/2009 18:51:18 »
You only need opposite steering when you're in a state of 'over-steer'  this is when the rear of the bike, or car, has lost grip and is sliding towards the outside of the curve. 
You need opposite/counter steering every time you have to make a bend, not only when you drive as a speedway bike...
If you don't believe me, take a bike, go at normal speed (not too low) and then steer, a little, towards left. Than tell me which way the bike goes.

What speed is 'too low' and why does it make a difference?  I can't say I've done much motorcycling, but I have done a lot of bicycling and haven't had to counter-steer.  Similarly, if this were to be the case on a motorcycle, when turning without loosing grip, why would it not be the case in a car?  I have done a lot of driving in cars and, as with the bicycles I've ridden, the only time I've had to counter-steer is when I've managed to unstick the rear wheels (in a rear-wheel drive vehicle).

You're not just referring to the inertial effect, which we counter by leaning, are you?
 

lyner

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Why does leaning a motorcycle make it turn around a corner?
« Reply #5 on: 31/05/2009 16:55:50 »
You only need opposite steering when you're in a state of 'over-steer'  this is when the rear of the bike, or car, has lost grip and is sliding towards the outside of the curve. 
You need opposite/counter steering every time you have to make a bend, not only when you drive as a speedway bike...
If you don't believe me, take a bike, go at normal speed (not too low) and then steer, a little, towards left. Than tell me which way the bike goes.
LeeE's right about the oversteer thing. That is another issue and applies with cars as well but, because the weight distribution is weird on a bike, the oversteer may be more of a problem. It's all to do with slip angles and tyre inflation and made worse by the fact that, once a bike leans and turns, the angle from vertical of front and back wheels is different,
We have done the bicycle steering thing to death and it hangs on the fact that bikes are all constructed with some castor angle to make them stable. If you just steer left and can't lean at all, then you will topple outwards (it may feel like you are turning right but it's just the bike leaning rightwards which gives this impression). If you lean over and don't allow the handlebars to turn, you will also fall over. The right design makes it feel natural both to lean and steer the appropriate amount. I imagine there is quite a lot of tolerance, in actual fact.
 

Offline lightarrow

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Why does leaning a motorcycle make it turn around a corner?
« Reply #6 on: 03/06/2009 22:30:45 »
You need opposite/counter steering every time you have to make a bend, not only when you drive as a speedway bike...
If you don't believe me, take a bike, go at normal speed (not too low) and then steer, a little, towards left. Than tell me which way the bike goes.

What speed is 'too low' and why does it make a difference?
It makes a difference because of gyroscopic effects. The value of the speed depends on a lot of things and so it's very difficult to establish a priori.

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  I can't say I've done much motorcycling, but I have done a lot of bicycling and haven't had to counter-steer.
Correct. With a bicycle is different. Probably because gyroscopic effects are still too low for that (but not for cycling 'without hands').

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  Similarly, if this were to be the case on a motorcycle, when turning without loosing grip, why would it not be the case in a car? 
Because a car has not nose cone shaped tires and because a car cannot tilt as a bike can do.

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You're not just referring to the inertial effect, which we counter by leaning, are you?
What do you mean with 'inertial effect'?
 

lyner

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Why does leaning a motorcycle make it turn around a corner?
« Reply #7 on: 04/06/2009 10:39:27 »
Bicycles are not usually driven at the same speeds around corners as motorbikes are. They are lighter and there is a lot less torque involved. Only real 'nutters' actually keep pedaling whilst going round a tight curve, whereas a motorcyclist will power round a curve - increasing the slip angle on the back tyre significantly. Also, because of the greater mass and 'footprint' of a motorbike, there is a lot more friction involved in the steering and the process is more damped.
If you simulate the 'speedway' effect with a mountain bike on gravel then you will easily get oversteer and this can only be countered by 'steering out'. There must be someone, with skill, who has personal experience of doing this in a controlled way. I, certainly have only managed to fall off in that situation - but the back wheel does 'break away' in the same fashion.

I don't like the word Inertia but I think it means the requirement to provide a moment (using weight force applied inside the curve from the point of contact with the road) to balance moment produced by the sideways force on the tyres which makes the bike turn. In other words, the "Inertia" of the bike, in the forward direction, would make the rider's body carry on forwards if the only force acting was sideways on the tyre, so he leans into the curve. This isn't a problem with 4 wheels but we still 'get thrown outwards' (owch!!!!) when going round a corner in a car.

To address the original post (not a wise move, I realise), I imagine, because of the wider and possibly smaller diameter tyres on a motorbike,  when leaning over, the contact point will change, laterally, much more than for a bicycle. This  would also change the geometry involved when leaning and, at first thought, it would seem that it could produce the required turning action - a sort of sideways castor effect, because the contact point is not in line with the 'equatorial plane' of the wheel. This castor angle would be several times the equivalent angle on a bicycle and the effect would be to pull the steering in the desired direction.

Motorcycling is a very 'physical' thing and the bike is a subconscious extension of the rider. How the process is described by an experienced motorcyclist may not be in line with the mechanical analysis of the situation. What we need is an Engineer Biker who can reconcile the subjective descriptions with mechanics.
 

Offline spag

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Why does leaning a motorcycle make it turn around a corner?
« Reply #8 on: 29/09/2011 04:05:33 »
I came across this in a google search. I realize I'm grave digging and for that I apologize, but perhaps I can give some useful information on this topic.

At speeds of around 10 - 15 miles per hour, counter steering takes effect. It's similar for every two wheeled vehicle I've come across, but its effects are much more pronounced on heavier vehicles. On a 100 pound scooter, I only had to hold onto the handlebars because that's where the controls are. Otherwise I could steer it by shifting weight. On heavier cycles, your mass affects it less, so you steer more using handlebars.

At the counter steering threshold, you'll notice that the bike will begin to track left for an instant before continuing in the other direction. I suppose that the farther from the threshold you are, the smaller the instant becomes, but I haven't quantified my observations or experimented. Going 60 miles an hour, I haven't been able to observe the instant where counter steering actually comes into play. I'm not sure what gyroscopic forces are, and I would really appreciate any insight in that area. At any rate, after that instant, it may be that your mass continues on its own path which results in the lean, and therefore steering.

Just leaning a bike over doesn't make it turn, not unless there's something badly wrong with its frame geometry.  The bike will only change direction if you move the handlebars, and you then need to lean the bike to keep the CoG over the path.  At low speeds the degree of lean is unnoticeable but at higher speeds the amount of lean required is obvious.

I am 90% sure you are wrong. This works on every vehicle with up to four pneumatic wheels, perhaps others, but I can't vouch for those from personal experience. Pneumatic tires have constantly changing contact patches. If one side of the tire is compressed, resulting in a smaller diameter of the patch on that side, and the other expands, as might happen in a lean, you'd have a cone-like contact patch. Cones roll in circles. I'm not sure how close to reality that idea is, so I'll throw another idea out: friction. Tires have inherent rolling resistance due to friction with the road and bearings. Should one side of your contact patch result in more friction than the other side, it may travel along a circular path rather than straight one.

An example of steering caused by lean in larger vehicles is camber steering. If your car is pulling to one side, often it's out of alignment. It could be the toe, but let's say your toe is spot on but your ball joints are worn, which result in a difference in camber across the front axle of 5 degrees. Your car will pull, even though the wheels are pointed perfectly straight ahead.


You only need opposite steering when you're in a state of 'over-steer'  this is when the rear of the bike, or car, has lost grip and is sliding towards the outside of the curve. 
You need opposite/counter steering every time you have to make a bend, not only when you drive as a speedway bike...
If you don't believe me, take a bike, go at normal speed (not too low) and then steer, a little, towards left. Than tell me which way the bike goes.

What speed is 'too low' and why does it make a difference? I can't say I've done much motorcycling, but I have done a lot of bicycling and haven't had to counter-steer.

It's more difficult to notice on bicycles because you dominate the bicycle. Try riding something that weighs twice as much as you. You could also find a nice hill to ride down and go about 20 miles an hour down it. Then push on your right hand grip without shifting your weight in anticipation of the turn. You are slightly beyond the threshold for counter steering, so your bike may briefly travel left, and then proceed right.

Quote
Similarly, if this were to be the case on a motorcycle, when turning without loosing grip, why would it not be the case in a car?  I have done a lot of driving in cars and, as with the bicycles I've ridden, the only time I've had to counter-steer is when I've managed to unstick the rear wheels (in a rear-wheel drive vehicle).

If I were to continue with my hypothesis that the contact patch from lean dictates direction on motorcycles, then I'd have to say it's because the contact patches on cars are usually almost static and balanced. Car steering wheels only change the direction of the contact patch (toe) and not the shape (camber).
 

Offline MikeS

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Why does leaning a motorcycle make it turn around a corner?
« Reply #9 on: 29/09/2011 08:08:16 »
"Countersteering is the act of turning a cycle's wheel away from the direction of an intended turn. This unbalances the bike toward the intended direction of turn, using centrifugal (centripetal) force and the bike's own forward momentum. Countersteering primarily uses the front wheel's trail as a lever arm to accomplish this. Countersteering is only that moment of unbalancing the bike, and completing the turn is simply called steering."
http://obairlann.net/reaper/motorcycle/beginner/countersteering.html
« Last Edit: 29/09/2011 08:15:58 by MikeS »
 

Offline yor_on

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Why does leaning a motorcycle make it turn around a corner?
« Reply #10 on: 29/09/2011 14:31:56 »
Don't recognize this from my bike. I lean towards the way I want to go, inwards (left) for a left turn, outwards (right) for a right turn, and as I remember it I don't turn the front wheel at all. The faster you go the lower you will lean towards the ground, until you come that low that something on the bike hits the tarmac, at which point you will lose traction if you're unlucky. So if I ever would to turn the handlebar the opposite direction of where I want to go? I don't know what would happen? Would I then turn into the bend even sharper than before. I don't think so myself? I think it would be a stupid thing to do..
 

Offline spag

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Why does leaning a motorcycle make it turn around a corner?
« Reply #11 on: 29/09/2011 19:41:07 »
Awesome, thanks MikeS.
yor_on:

Notice that the wheel doesn't actually turn, it stays straight, but the bike leans.
« Last Edit: 29/09/2011 19:43:50 by spag »
 

Offline yor_on

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Why does leaning a motorcycle make it turn around a corner?
« Reply #12 on: 30/09/2011 13:44:20 »
Yeah, that could explain it. The pressure I put on the handlebar might be unconscious, but as far as I remember I do not see the wheel turned any which way as I lean into a curve. And if you really turned that wheel the opposite of your leaning into that curve, I doubt it would give you a counter steering effect, but I do expect you to crash.
 

Offline Krotovina

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Re: Why does leaning a motorcycle make it turn around a corner?
« Reply #13 on: 09/12/2012 04:54:42 »
This discussion is hilarious.  A motorcycle turns when you lean it, either by counter steering or leaning over, because motorcycle tires have unequal radius, ie, they are narrower on the outside than the center.  Another way to think of a motorcycle tire is two truncated cones joined at the fat end.  When a bike is leaned it is running on a truncated cone with the larger radius near the middle and the smaller radius near the inside.  Since the large radius and the small radius are turning at the same number of revolutions, the center part of the tire covers more distance and the bike turns towards the smaller side, i.e. the inside.  This is easily demonstrated with truncated cones, or rubber doughnuts.   
 

Offline lightarrow

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Re: Why does leaning a motorcycle make it turn around a corner?
« Reply #14 on: 09/12/2012 21:11:45 »
The discussion was also about how you can lean the motorcycle. At high speeds you can't do it, if you don't countersteer (wheels angular momentum).
 

Offline David Cooper

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Re: Why does leaning a motorcycle make it turn around a corner?
« Reply #15 on: 09/12/2012 21:55:37 »
If you need to make a fast maneouvre, you can't afford to wait for the bike to lean the way you want to turn, so you steer the other way to unbalance it to help it lean the way you want it to. If you simply steer the way you want to go, you'll put your weight to the wrong side of it and make the turn even slower as you'll then have to correct that as well. Just turning the steering doesn't make the bike lean over, so the idea that a reduced radius part of the tire comes into contact with the road just by turning the steering is wrong.
 

Offline lightarrow

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Re: Why does leaning a motorcycle make it turn around a corner?
« Reply #16 on: 10/12/2012 20:25:51 »
Just turning the steering doesn't make the bike lean over,
Did you try?
 

Offline David Cooper

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Re: Why does leaning a motorcycle make it turn around a corner?
« Reply #17 on: 10/12/2012 21:36:40 »
Just turning the steering doesn't make the bike lean over,
Did you try?

Extensively, on a bicycle. Turning the steering causes the front wheel to run to one side (whichever way it's pointing), and it's only once it has moved to the side and your centre of mass (including mass of the machine) is off centre that this imbalance causes the bike to start to lean over in the opposite direction to the way you've just steered.

If you really want to explore how it works though, you need to learn to ride a bicycle with your hands off the handlebar as this slows the initial turn down considerably - you don't entirely have to wait until the bike falls the right way, but you can move your weight about on the bike to force it to lean and use that lean to turn the steering, and it's only after you've steered it that the weight imbalance comes into it and the bike and rider collectively start to lean the opposite way from the way the bike has just been steered. To see the effect best though, you do need to practise a lot - I can go round in tight circles at very slow speed with my hands off the handlebar because I virtually lived on a bicycle as a child and spend thousands of hours doing this. You also need the right frame geometry though - some bikes are easy, but others are near impossible.
« Last Edit: 10/12/2012 21:38:32 by David Cooper »
 

Offline lightarrow

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Re: Why does leaning a motorcycle make it turn around a corner?
« Reply #18 on: 12/12/2012 15:47:54 »
Just turning the steering doesn't make the bike lean over,
Did you try?

Extensively, on a bicycle.
But a bike it's not a bicycle. Try with a bike. At high speed, you only need to make a slight rotation of the handlebar, so slight you don't even notice with the eye, to feel the bike going down in the opposite side.
Quote
Turning the steering causes the front wheel to run to one side (whichever way it's pointing), and it's only once it has moved to the side and your centre of mass (including mass of the machine) is off centre that this imbalance causes the bike to start to lean over in the opposite direction to the way you've just steered.

If you really want to explore how it works though, you need to learn to ride a bicycle with your hands off the handlebar as this slows the initial turn down considerably - you don't entirely have to wait until the bike falls the right way, but you can move your weight about on the bike to force it to lean and use that lean to turn the steering, and it's only after you've steered it that the weight imbalance comes into it and the bike and rider collectively start to lean the opposite way from the way the bike has just been steered. To see the effect best though, you do need to practise a lot - I can go round in tight circles at very slow speed with my hands off the handlebar because I virtually lived on a bicycle as a child and spend thousands of hours doing this. You also need the right frame geometry though - some bikes are easy, but others are near impossible.
I think you're right, but I'll think about it more.
It's likely that both effects are present and the gyroscopic one prevails at greater speeds.
« Last Edit: 12/12/2012 15:57:16 by lightarrow »
 

Offline David Cooper

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Re: Why does leaning a motorcycle make it turn around a corner?
« Reply #19 on: 12/12/2012 23:44:32 »
But a bike it's not a bicycle. Try with a bike. At high speed, you only need to make a slight rotation of the handlebar, so slight you don't even notice with the eye, to feel the bike going down in the opposite side.
At high speed (which can be achieved on a bicycle by bombing down a steep hill) it only takes a tiny adjustment too, because that steers the front end of the bicycle to one side massively more quickly than at low speed, thereby placing the centre of mass of rider plus bike to the side, and that translates to a lean and a turn without bringing gyroscopic effects into it. It may be though that there is some additional gyroscopic aspect that amplifies the effect, though I'd have thought that if there was one it would be to allow you to take a corner without bothering to leaning over (or possibly even while leaning the wrong way). A simple way to test the gyroscopic effect on steering with a motorbike though would be to do a slight wheelie and turn the steering - that would eliminate the effect of the wheel running to the side and leave any tilt entirely down to gyroscopic effects. Anyone able to test that legally?
« Last Edit: 12/12/2012 23:46:28 by David Cooper »
 

Offline lightarrow

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Re: Why does leaning a motorcycle make it turn around a corner?
« Reply #20 on: 13/12/2012 15:41:06 »
At high speed (which can be achieved on a bicycle by bombing down a steep hill) it only takes a tiny adjustment too, because that steers the front end of the bicycle to one side massively more quickly than at low speed, thereby placing the centre of mass of rider plus bike to the side, and that translates to a lean and a turn without bringing gyroscopic effects into it. It may be though that there is some additional gyroscopic aspect that amplifies the effect, though I'd have thought that if there was one it would be to allow you to take a corner without bothering to leaning over (or possibly even while leaning the wrong way). A simple way to test the gyroscopic effect on steering with a motorbike though would be to do a slight wheelie and turn the steering - that would eliminate the effect of the wheel running to the side and leave any tilt entirely down to gyroscopic effects. Anyone able to test that legally?
a wheelie put where and how? I don't visualize your idea.
 

Offline David Cooper

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Re: Why does leaning a motorcycle make it turn around a corner?
« Reply #21 on: 13/12/2012 19:23:31 »
a wheelie put where and how? I don't visualize your idea.

If the gyroscopic effect is significant in helping a bike turn, there's an easy way to test that while eliminating the other effect of the rotation of the slightly-steered-to-the-side wheel dragging the front of the bike to one side. The experiment could be done simply by driving along at high speed in a straight line, then doing a slight wheelie to get the front wheel off the road, and then the steering can be turned a little. If there is a gyroscopic effect from that which leads to the bike tilting over the other way from the way the wheel has just been steered, it will indeed lean over and that will be a positive result for the experiment. Expert biker and closed track (for legal reasons) required.
 

Offline David Cooper

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Re: Why does leaning a motorcycle make it turn around a corner?
« Reply #22 on: 14/12/2012 18:58:54 »
Something that makes me suspicious of the idea that there's a significant gyroscopic aspect is that if it makes the bike lean over more strongly to the right when you initiate the turn by steering a little to the left, once you've started the turn and turned the steering over to the right instead, an opposite gyroscopic effect should kick in strongly and cause an equally strong or stronger effect to eliminate the lean that the original gyroscopic effect generated, thus removing all advantage and possibly making things worse rather than advantageous.
 

Offline lightarrow

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Re: Why does leaning a motorcycle make it turn around a corner?
« Reply #23 on: 24/12/2012 11:48:49 »
I think you wrote quite convincing arguments...
 

Offline David Cooper

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Re: Why does leaning a motorcycle make it turn around a corner?
« Reply #24 on: 24/12/2012 20:51:49 »
Maybe so, but that's not good enough for science: the experiment is always king. I don't think bicycle wheels are heavy enough relative to weight of rider-plus-rest-of-machine to answer the question, so there's no alternative to finding a biker who's skilled enough to try it out and who has access to a runway or track (that isn't an open road) where it could be legal to do the experiment. I'm sure that any one who races motorbikes would be able to do this, so if anyone reading this knows such a person, please ask them, but warn them that it might be dangerous if the gyroscopic effect is significant - start with very slight turning of the steering while doing a wheelie at high speed and gradually try turning the steering further (and doing it faster) over time once accustomed to the behaviour of the system up to that point. I don't want anyone to get hurt doing this.
 

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Re: Why does leaning a motorcycle make it turn around a corner?
« Reply #24 on: 24/12/2012 20:51:49 »

 

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