Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: chris on 28/05/2009 04:08:57
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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?
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?
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.
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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.
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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.
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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?
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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.
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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.
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').
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.
You're not just referring to the inertial effect, which we counter by leaning, are you?
What do you mean with 'inertial effect'?
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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.
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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.
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).
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"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
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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..
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Awesome, thanks MikeS.
yor_on:
Notice that the wheel doesn't actually turn, it stays straight, but the bike leans.
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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.
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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.
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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).
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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.
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Just turning the steering doesn't make the bike lean over,
Did you try?
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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.
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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.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.
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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?
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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.
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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.
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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.
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I think you wrote quite convincing arguments...
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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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With a bicycle, it is certainly possible to steer it with leaning alone.
I think part of it has to do with the fork rake. If the headset was perfectly vertical, and the forks had no rake, then leaning the bicycle would do nothing.
Having the forks raked backwards, like on a shopping cart, works well for the wheels to follow the turn when the cart is kept vertical.
Likewise, on a tadpole trike, one may choose a rearward rake as the trike doesn't lean, and thus one would choose wheels to follow the direction of motion.
On a bicycle, I think the forward angle of the headset and rake of the fork acts to make the wheel turn towards the direction it is leaning which may, in fact, help with balance.
Rake, of course, can be achieved with bending forward anywhere below the headset, or even with merely the bolt location on the forks.
It may be a combination of things, so that the round tire may work in conjunction with the fork geometry to turn the wheel.
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Why does leaning on a motorbike cause it to turn?
Don't know. Great question though. It has to do with gyroscopics. The wheels act like gyroscopes.
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?
Yes. That little fact saved my life many moons ago.
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Why does leaning on a motorbike cause it to turn?
Don't know. Great question though. It has to do with gyroscopics. The wheels act like gyroscopes.
I suspect you didn't read through the thread. Out of interest though, if you don't know the answer, why do you then immediately go on to state an answer as if it's a truth? This idea of it being due to gyroscopic effects may be nothing more than a meme.
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Ok,
I started thinking about some of the bicycle geometry a little bit more.
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The weight vector comes essentially straight down from the hub, going through the center of the point of contact between the tire and pavement when the bike is vertical.
The headset is tilted forward, creating a tilted line which is the axis of steering rotation which lies in front of the weight vector.
When you lean the bicycle, say leaning it to the right, that creates a crosswise force on the tire to the left.
Because this crosswise force is being applied to the tire behind the axis of steering rotation, it tends to kick the point of contact between the pavement and the tire out to the left, turning the forks to the right, and causing the bicycle to turn to the right.
Raking the forks forward brings the weight vector forward, towards the axis of steering causing the bicycle to be less responsive to leaning. One should be careful to make sure it is not pushed in front if the axis of steering rotation (aligned with the headset), otherwise it would make the bicycle steer away from the lean, and make it very unstable.
I think there is another benefit of raking the forks forward in that it creates an upward vector (I think) that tends to self correct the steering, and make the bike tend to ride more in a straight line.
You can create an equivalent fork rake with any method to bring the hub to the same spot in front of the axis of steering through the headset.
The round tire merely gives good surface contact and maximizes grip throughout the turn which is especially important as both the lean and centrifugal force tends to cause the tire to slide away from the lean (in the above example, to the left).
The advantage of this complex geometry is that it when turning, one leans the bike in the direction of the turn so that the centrifugal force vector of the turn plus the weight vector equalize to go through the axis of the frame. In fact, if you lean too much, it would tend to cause the bike to turn towards the lean, and increase the centrifugal force vector to right the bike. If you don't lean enough, it would cause the bike path to straighten.
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I've noticed this is a really old convo but since it looks like the answer hasn't really been found and I was searching through Google a bit myself to find the answer when I found this site, I'll tel you why I think people tell you to counter steer motorcycles.
First, you counter steer into the turn to tilt the bike in the correct direction ( let's say you want to go right), because as the wheels turn left, the center of mass tries to stay where it is meaning that you are now tilted right (you can see it in cars taking very tight turns as well, the wheels on the inside of the turn even leave the ground sometimes) You didn't actually go anywhere, but the bottom of the bike pivoted around you and is now to your left, meaning you are leaning to the right. you do this to lean because most bikes are much heavier than you are, unlike bicycles where you are the heaviest thing on it. Lighter motorcycles don't really need to be counter steered since you can still force the bike into a lean
Now, why does leaning make you turn? It does this because unlike cars, motorcycle tires are shaped like donuts, and if you cut a donut into slices like a pizza, you will notice that the farther you lean the slice you cut to one side (let's say right), the shorter the surface in contact with the road on the right is compared to the left, because the closer you get to the place where the "pizza" slices meet the more the slice tapers to a point. Now what this means is each turn of the wheel makes the left side of the tire travels further than the right side, since the right side is basically a smaller circumference because of the way the tire is shaped. So as the right side lags behind, the bike turns right.
OK, that's cool, but why do people say you have to counter steer IN the corner as well? Now THIS is the part where the gyroscopic effect comes in. Because the gyroscopic effect of tires increasing the bigger they get, you start to notice on motorcycles, especially bigger ones, that the bike is trying to level itself throughout the turn. On smaller bikes the effect isn't too noticed because the tires ase lighter and have less effect and the bikes themselves are lighter so you can just use your own strength and weight to keep it in the lean. On bigger bikes you continue to counter steer, which just like when you started the turn, pulls your tires further left out of the turn causing you to lean more right and cancel the gyroscope trying to level you out. Once you're done turning, you either keep the bars straight and wait for the gyroscopic effect to straighten you out or turn right into the turn which brings your tires back under you and then straighten out.
You turn like this on bigger bikes instead of just turning right to go right because doing that at the speeds you're going with a vehicle much heavier than a normal bicycle heavily increases your chances of flipping the bike, and unless you're strong and heavy enough to stop the bike from leaning the way I described above, you'll just end up going the wrong way anyway
Hope this helps someone who finds this topic two years from now like I did, and hopefully you know what to do with my example to make the bike turn left as well ;P
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I see this thread has been left to die several times only to be jolted back to life time and time again, so allow me to get the defibrillator out once more.
This question I have been searching for the answer to for over 10 years and I have invested a significant amount of thought and research onto trying to understand it over this time and I have to say I am not even remotely convinced by any of the suggestions posted in this thread thus far. In fact, after considerable investigation, I am inclined to think it is simply a mystery :O
I mean no offence to previous posters but I will first go through and dispute each of the theories proposed so far...
Before I rip though let me clarify a little of the discussion about counter steering.
Firstly I have to assert that counter steering is absolutely, definitely, 100% a thing! On occasion people will try and say it does not exist, or at the least assert that they do not use it but this is simply not the case. Absolutely everyone who has ever ridden a single tracked, two wheel bike has used it. It makes no difference if the bike is a motor bike, a pushbike or even a childs scooter. Counter-steering is fundamentally the mechanism through which a turn is initiated (and also concluded). It also matters not how fast nor slow you travel nor does it matter what the mass of the vehicle may be. Counter-steering, fundamentally, is the means by which the lean of a bicycle is controlled.
To illustrate, let us imagine a rider making a turn to the right. To make the turn one must first push a little with the right hand causing the front wheel to turn to the left which in turn causes the front wheel to track to the left resulting in first the front but then the rear wheel tracing out to the left. This causes the center of mass of the rider and bike to fall entirely to the right-hand side of the wheel track which invariably causes the bike and rider to lean (or fall) to the right. You can think of tracking the wheels to the left as being like slipping on a banana peel or sweeping out an old mans walking stick. If your feet are swept out from underneath you to one side you will fall to the opposite side. Once the lean has been initiated (through counter-steering) the rider must turn into the corner a little in order to "hold the lean angle" and prevent the bike from falling over. Note the amount by which the rider steers into the corner is very minimal and the deviation in steering angle is much less than that of the angle of curvature around the circumference of the turn itself. Finally at the end of the turn the rider will actually turn more strongly into the turn causing the wheels to once again track underneath the rider thus standing the bike and rider upright again like an inverted pendulum. So, in summery a right turn is initiated with a counter-steer to the left, it is held with a slight right turn and ended with a sharper right turn to stand the bike upright again.
There are countless examples on YouTube, but here is one of the better ones:
If anyone doubts the existence of counter-steering on a pushbike I invite you to try lightly holding the right handle grip with the fingers of the left hand. Although most of us are unaware of the minor corrections we give a bike to remain stable once you reach across and hold with your opposite hand you'll very quickly become aware of them, and once you are aware of them you quickly realize all these adjustments are in fact "counter-steering" inputs. I was most surprised when I first tried this myself. Be advice though it is very easy to get confused so only do it at a relatively slow speed and be prepared to let go and grab with your normal hand the moment things get uneasy.
But on with the main question at hand:
First point I will refute is the argument of gyroscopics. Gyroscopics is a frequently misunderstood and magical seeming force so not surprisingly all manor of bizarre effects are often attributed to it. While it is true that gyroscopic precession will cause the axle of a rotating body to precess or turn when the wheel leans and this indeed has an affect on bicycle dynamics this is not the principle means by which a bicycle turns. For one, precision would only be present while the bike leans in and leans out, and would not be present through the main course of the turn when the lean angle is relatively constant. Also, if the turning of a bike were governed by the procession of wheels the wheels would precess one way while leaning in and precess in the opposite direction by the exact same amount when returning to vertical, which would result in an 'S' track but would always end with the wheels heading in the same direction they started. Note that while gyroscopic forces are also the favorite high school physics explanation as to why a bicycle stands up when you ride it but falls when your stationary, unfortunately gyroscopic forces really don't explain it at all. In school they then love to show you the experiment of spinning a wheel then dangle it from a piece of rope attached from one end of the axle and show how it 'magically' stays upright. This is an impressive and dramatic experiment but unfortunately it really doesn't have much to do with bicycle stability at all. In fact the "gyroscopic" explanation for stability was conclusively dis-proved in the 1970's when a couple of physicists built a bike with counter rotating weights designed to completely cancel out the gyroscopic effects of the wheels and preceded to ride the bike with relative ease. In fact the reason bicycles are self stabilizing is actually still a mystery, and anyone who tells you otherwise is misguided.
For anyone interested here is an excellent paper by some egg heads at Cornel that systematically disproved all known theories for bicycle stability: http://bicycle.tudelft.nl/stablebicycle/StableBicyclev34Revised.pdf
In regard to the "conical profile" argument I again say it seems like a good argument at first but doesn't really hold up under further scrutiny. I can give several counter arguments but two simple ones are that the camber of roads does not much affect steering and ridged sharp edge disks (like coins) still turn when they lean.
If you look closely you will notice most roads are not flat at all and are in fact significantly higher in there center than at their edge. This is to facilitate water run off. As a consequence, when riding in a straight line you are rarely riding on the center of the tyre. In fact every time I replace my front tyre it is always noticeably more worn right of the center line than it is on the left (I assume those from the land of the free and home of the brave wear the left side of there tyres). If this "conical profile" theory were the main course for a bike to turn than I would constantly be fighting my bikes natural tendency to pull over to the other side of the rode. I in fact tried an experiment one time where I lent my bike over to a significant angle and was able to keep it tracking straight by hanging significantly off the other side. It wasn't an overly scientific test and I felt really silly doing it but I was able to demonstrate to my self that a bike will indeed still travel straight even if leaned at a significant angle if the center of gravity is still essentially upright. Also, if the "conical profile" theory were indeed the reason bikes turn than the camber often built into road corners would in fact have a adverse affect on bikes rather than assisting them, which is clearly not the case. If bikes were to perform better on inverse cambered corners velodromes would be designed with outward sloping berms. Can you imagine it?
The other counter argument I'll mention is that of a coin rolling across a table. While the coin is upright the coin rolls straight but if the coin leans over the arc of travel curls around in the direction of inclination. Obviously the edge of a coin is fairly sharp and unless you argue that the corner is rounded at a microscopic level there really is no difference in the rolling diameter of the inside edge and outside edge of the contact patch, yet still the coin curves.
Wow, this post really is getting long and it's now getting late here so I think I'll call it a night.
It's been a good read fellers and hopefully someone will one day work it all out ;)
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ReyD - Welcome to the forum.
If you're interested in this subject then see - http://en.wikipedia.org/wiki/Countersteering
I know from first hand experience just how important this is since this knowledge saved my life once.
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Newbie, this one is still not answered clearly, IMO.
The reason a MC turns when you lean is because of the laws of physics. if you roll a coin, flat washer or any other disc-shaped object across a table, what happens when it starts leaning? It turns in the direction of the lean. Nothing to with the shape. If coin or washer flat on the bottom, it will stand on its edge, and turn! You have one force moving it forward and one force (gravity) trying to pull it over. The torque created causes it to turn.
A MC going down the road at speed has two gyroscopes on it called wheels. Those spinning wheels want to keep the MC as it is just like gyros stay as is even if the pivot point of the axis is moved. It's the same reason it's easier to balance a bike at faster speeds. It takes more force to overcome the gyro effect. It's also why all the cool kids could ride bicycles with no hands on the handlebars. As long as there is not force to change it, physics demands that goes as it is going.
As to counter steering, yes it is absolutely VERY real. A simple experiment: Stand straddle of a bicycle and balance it with single finger on the goose neck, what would happen if you pushed the left handlebar forward? Yes, it would fall and hit your left knee. Pushing only the slightest bit forward would cause this. With a single linear axis of wheels like a bicycle or motorcycle, the slightest tip off center starts the bike tumbling to the ground. Counter steering is simply producing that effect. By varying the forward pressure on the handlebar, you are controlling the balance between the gyroscopic effect of the wheels in keeping it as is and it falling over. As it leans, it turns as described above.
The lean also keeps the CG such that you are not flung off the machine.
Why counter steering verses leaning? Safety. As a 25+ year veteran of motorcycling, I can firmly attest to the fact that a quick forward thrust on the bar at speed will cause the motorcycle to make an adjustment in direction FAR more quickly than you can attempt to lean your body weight and turn the bike. Approaching a curve, this probably doesn't matter, but dodging a car or obstacle in the road it absolutely does. Training your brain to think like this and developing your riding skills with counter steering in mind will make you a MUCH more capable operator.
FWIW, Motorcycle tires are rounded to maintain surface contact to the road WHEN the bike leans to turn. You could ride a bike with tires made like car tires and turn it just fine. It just wouldn't be very safe.