What is countersteering anyway?
Posted September 10, 2003
Updated December 28, 2004 Introduction
This is such a common question, and one which raises so much contentious argument, that it seemed worth offering my well-reasoned opinion on the subject. Of course, it is all just opinion, as I haven't performed the repeatable experiments necessary to prove
what I'm about to write. Note that this article is equally applicable to motorcycles or bicycles, although it's harder to be conscious of countersteering a bicycle due to its relatively light weight.
That said, here's the basic idea of countersteering, on anything with two wheels: when you're going in a straight line, the handlebars are centered; when you want to turn, you actually have to turn the handlebars in the wrong direction first, to lean the bike over, then you steer into the turn to keep the bike from flopping completely over. The part where you steer in the wrong direction to make the bike lean over is called "countersteering."
Why is countersteering important? Because it's the only way to turn a moving, two-wheeled vehicle. If you're doing it unconsciously, by thinking "steer left" or shifting your weight, or putting more pressure on one peg/pedal or the other, that's not very efficient. If you do it consciously, you can steer your bike with amazing speed and accuracy, which could very easily save your life one day. Kids on bicycles
Most people who ride motorcycles also learned to ride bicycles at some point in their lives. Some of you may have also more recently taught a child how to ride a bike. Learning how to ride a bike is really hard! You probably spent some time with training wheels on your bike, leaning hard into them going around corners.
The human mind doesn't readily encompass the idea of turning the wrong way in order to go the right way. When you were a kid, and wanted to turn right, you swung the bars over to the right, exactly as is sensible. Only, when you did that (keep in mind, you were going at a low speed), the bike fell over to the left, hopefully onto the training wheels.
We all called it "learning to balance" when I was learning to ride a bike. I thought of it as gaining some kind of magical sense of balance, as if my natural ability to stand upright was somehow discarded once I got on a bike. You may see where this is going. Of course, I still knew how to balance, but I didn't know how to countersteer
. Most dads don't know that that's what they need to teach, but that's exactly what a kid has to learn to ride his bicycle.
Without learning the counterintuitive act of steering in the wrong direction, no one can figure out how to ride a bicycle. That's the magic switch that goes off in your brain, and suddenly allows you to ride the bike. I bet if you think back, you probably spent some time swerving your handlebars back and forth, marvelling at the weird feeling of turning contrary to which way the front wheel was pointing. Steering while moving
When your bike is moving, there are a couple of factors keeping it upright and running in a straight line. The front end's trail (which is the distance between the steering pivot point and where the wheel actually hits the ground) provides a castering force, like the wheels on a rolling office chair. The rotating wheels are big gyroscopes -- just like a child's toy gyroscope, they will try to stay upright (and thus not steer in any direction other than straight). If you started your motorcycle or bike rolling on a straight road without a rider, it wouldn't fall over until it ran out of speed or hit something.
When the bike slows down enough to fall over, that's because the lower the speed, the less force both trail and the gyroscopic forces exert. At some speed, the not-precisely-balanced weight of the bike overcomes the amount of force exerted by the trail and gyro forces, and gravity wins.
In order to make the bike turn, you have to unbalance it. The only way to unbalance a bike at speed is through countersteering. No matter how far you lean off the bike, it's not going to change direction: the forces keeping it upright are too strong. [Update Dec. 2004: this statement is incorrect -- I've steered my Ninja by leaning off without handlebar input, but it's really
slow to react. The principle, especially for beginners, is still sound, though.] However, if you turn the handlebars in one direction or another, the bike immediately unbalances away from the direction you turned. Centrifugal force pulls the bike sideways, and since the tires are "stuck" to the ground, the bike naturally pivots around them, to lean over away from the turn. Once you've achieved the lean angle you desire, you turn the handlebars back in the direction of the turn to prevent the bike from flopping completely over onto its side. This process of steering away from the turn then into it usually happens so fast that by the time you notice what's up, you're steering into the turn, and thinking I'm a crazy man.
However, next time you're travelling at speed (over about 30 MPH on a motorcycle, or as fast as you can get going on a bicycle) and traffic around you is very sparse -- ideally on a completely deserted road -- try pushing on one side of the handlebars. Just a slight and even pressure on one side. The bike will immediately start leaning toward the side you were pushing on. Now, try pushing on the other side. The bike stands right back up. That's the essence of countersteering.
Now, this is the part where many people call "bullfeathers!" on the whole countersteering thing. Most experts explain countersteering as if it were the only thing in the world you needed to know about steering a bike. It's not
. You use countersteering to lean over, and then, most of the time, you steer into the turn! Countersteering is mostly useful for getting you leaned over, a great deal of the time. (Note that at high enough speeds, you actually countersteer all the way through a turn, because the higher the speed, the stronger those upright-pulling forces are. But that's a different thing, I'm writing for street riders, not racers; go away kid, you bother me.) Slow-speed countersteering
All of this applies to low-speed steering as well, all the way down to a dead stop (but see below for the "dead stop" discussion). If you're rolling at all, the only way to steer a bike is to get it leaned over in the direction you want to turn, at least a little tiny bit, or when you turn, the centrifugal force will flop the bike over to the outside of the turn.
So, to cause the bike to lean in the direction you want to go, you have two choices at low enough speeds (like, below about 7 MPH on a motorcycle): you can countersteer, or you can lean your body weight to the side you want. Leaning yourself over works at this point because the force of gravity acting on your body is stronger than the upright-pulling forces described above (remember that they get stronger as speed increases, so they get weaker as you go slower).
works, all the way down to a complete stop. You can practice by finding a big empty parking lot again: get the bike rolling in first gear, and let the engine settle down to idle speed (hopefully your parking lot is flat). Carefully take your weight entirely off the handlebars, and push gently on one side. Whichever side you push on, the bike will immediately lean toward it. Go as slow as you can, and try it (but don't push very hard). Countersteering still works.
I think the reason many people claim countersteering "starts" around 10 MPH is that they can make the bike turn without using countersteering below that speed. While it's true that you don't need
countersteering to steer while going slowly, you can still use
it. Steering from a stop (U-turns)
If you're sitting stopped somewhere, and want to make a quick U-turn, you're not going to use countersteering. The whole point of countersteering is to take the bike from being perfectly vertical, to being leaned over. When you're sitting on the bike, stopped, you can use your leg muscles to lean the bike over, before you start going. Then, once you're moving, you steer into the turn, just like you'd expect.
So, countersteering doesn't have any meaning from a stop, you only want to use it once you're rolling. A little thought experiment
And finally, for the Doubters among you, I propose a thought experiment (note: I don't recommend trying this for real, because it will probably break your bike and might break you).
Imagine that you're sitting on your bike, stopped. I walk up and say "ooga booga!" and put a magic spell on your bike (thought experiment, remember), so that you cannot turn the handlebars to the right, past the center point. You have full movement of the bars from center to the left lock, but when you hit center, the bars absolutely won't move any further.
Now, imagine holding the bike straight upright, no leaning to the left. Start it moving, with you on board. You cannot turn the handlebars to the right at all. Really put yourself mentally on this vehicle, with the steering "broken" as I describe.
How long do you last, going as slow as you can, before the bike flops over onto its right side? Does even thinking about this make your body get squirmy and uncomfortable? It does for me -- my body knows from riding bicycles and motorcycles that if something happened and my steering got locked in the manner I just described, I'm screwed
. I'll be falling over to the right so fast, I'll be lucky to escape without a broken leg, no matter how hard I lean my body to the left once I'm going.
Now, imagine the same thing, but you're going at high speed (say, 25 MPH on a bicycle, or 60 MPH on a motorcycle) when the steering suddenly "breaks" so you can't turn the bars right. It's a little bit more stable, but as soon as anything makes you want to steer, you're screwed. This brings up vivid memories of bicycle crashes when I was young, for me.
The point of this thought experiment has hopefully been clear. If you can't countersteer your two-wheeled vehicle, you're going to fall over.
I hope this clarifies what countersteering is, and what it isn't. This is a subject that you can't just think your way through without any practical experience. Go grab your bicycle or motorcycle and really think about what you're doing, as you ride. Find a big empty parking lot and actually practice steering with and "without" countersteering (whatever form that "without" may take for you). Try leaning your body. Try snapping the bike over by countersteering. It really works, and it's really really effective. Get yourself to the point that you naturally and instinctively countersteer. It's the only way to quickly and precisely steer a bicycle or motorcycle, and it can easily save your life.
by Ian Johnston
OR IF YOU PREFER
By James R. Davis
Everyone who has driven a motorcycle has experienced it, the MSF classes mention (but don't explain) it, and motorcyclists discuss it all the time. But what is it, really? How does it work? Why does it work? All questions I will try to deal with in this discussion.
At very slow speeds we steer a motorcycle by turning the handlebar in the direction we wish to go. We can only do that at speeds of less than about 5 MPH. At any higher speed we do the exact opposite, whether we realize it or not. For example, assuming we want to turn to the right, we actually TRY to turn the handlebar left. This results in the front wheel leaning to the right and, as a result of the lean of the wheel, a turn to the right. This is counter-steering.
Why is it that we don't get confused regardless of our speed? Because we have learned that steering a motorcycle is an effortless chore. That attempt to turn the handlebar to the left FEELS like we are pushing the right grip rather than pulling on the left one. It feels like that because the harder we push it, the more the motorcycle turns to the right and, thus, it feels like the right grip is pushing back at you that much harder. In other words, we quickly learn to associate counter-steering feedback with the hand closest to the direction in which we wish to turn. Further, even a little bit of experience shows that counter-steering is essentially effortless while trying to turn the handlebar in the direction you want to go is virtually impossible. Humans are relatively fast studies, after all.
It takes only a modest familiarity with a gyroscope to understand counter-steering - at least to understand how most people believe it starts to work. The phenomenon is called Gyroscopic Precession. This is what happens when a lateral force is applied to the axis of a spinning gyroscope. The spinning gyroscope translates the force vector ninety degrees off the direction of spin. Thus, if we try to turn our front wheel to the left, the force we use appears as a lateral force forward against the axle on the right side and this is translated into a force that tries to lean the wheel to the right. Similarly, trying to turn the wheel to the right results in the wheel trying to lean to the left.
But gyroscopic precession is not a necessary component of counter-steering. No matter how slight, if your front wheel deviates from a straight path your motorcycle will begin to lean in the opposite direction. It is entirely accurate to assume that even without gyroscopic precession, the act of steering the front wheel out from under the bike would start counter-steering in the opposite direction. This is a result of steering geometry - rake. You can observe it at a complete stop. Just turn your handlebars in one direction and you will see that your bike leans in the opposite direction as a result. [Please note that though gyroscopic precession is not a necessary component of counter-steering it GREATLY facilitates it. Indeed, it is the precession of the REAR tire that results from the momentary change of direction of the bike that 'pushes' about 80% of the bulk of the bike into a lean in the direction you want to go.]
In the case of a motorcycle, your handlebar input is immediately translated by gyroscopic precession into a lean in the opposite direction. Since your front wheel is attached to the bike's frame, the body of the bike also attempts to lean. It is the lean of the BIKE that overwhelms the handlebar effort and drags the front wheel over with it - gyroscopic precession merely starts the process and soon becomes inconsequential in the outcome.
If, for example, you had a ski rather than a front wheel, the front would actually begin to turn in the direction of handlebar input (just like it does with a wheel instead of a ski) and body lean in the opposite direction would then overwhelm that ski making counter-steering still effective.
The ONLY WAY to turn a motorcycle that is moving faster than you can walk is by leaning it (if it only has two wheels). We have talked only about what starts that lean to take place. Indeed, all we have talked about is the directional change of the front wheel along with the simultaneous lean of the bike, both in the opposite direction signaled by handlebar input. So then what happens?
Before getting into what is actually somewhat complicated let me say that if you were to let go of your handlebars and provide no steering information whatever (or you were to get knocked off your motorcycle), after some wildly exciting swings from side to side your motorcycle would 'find' a straight course to travel in and would stabilize itself on that course, straight up! That's right, your motorcycle has a self-correcting design built into it - known as its Steering Geometry - that causes it to automatically compensate for all forms of leaning and speed changes and end up standing straight up, going in a straight line, whether you are on the bike or not - until it is traveling so slowly that it will fall down.
This diagram shows a typical motorcycle front-end. The handlebars are connected to the steering column, which is connected to the knee bone, which is... Oops, wrong discussion. The steering column (actually called the 'steering stem') does not connect to the knee bone, nor does it connect directly to your forks! Instead, it connects to what is known as the triple-tree (shown as D in the diagram.) This is merely where both forks are tied, along with the steering stem, to the bike's frame. You will notice that the triple-tree extends towards the front and that as a result the forks are offset forward some distance from the steering stem. (Notice the red diagonal lines marked C and C'.) This is known as the offset.
Now please notice that the forks are not pointing straight down from the triple-tree, but are instead at an angle. This angle is known as the rake. Were it not for that rake (and modest offset) the front tire would touch the ground at point A. (Most rake angles are approximately 30 degrees.)
What the rake does for you is profoundly important. For one thing, it causes any lean of the wheel to be translated into a turn of the wheel towards that lean. For another, it slows down your steering. That is, if you turn your handlebar 20 degrees at slow speed your course will change something less than 20 degrees. [At higher speeds you NEVER would turn your handlebars 20 degrees - the front wheel is always pointing virtually straight ahead.] Rake, in the case of higher speed turning then really does SLOW DOWN the realization of the turn. (We will see why soon.)
Looking at the diagram, imagine that instead of pointing to the right the wheel is pointing straight at you. (The body of the motorcycle remains pointing to the right.) You will now recognize that the contact patch which was B before the wheel turned has now got to be near where C' is at. In other words, the fact that your wheel is on a rake results in the consumption of part of your steering input into a displacement of the contact patch of the wheel. (This is why steering is 'slower' - and the greater the rake, the slower it is. Note that 'slow steering' is NOT the same as 'under-steer'.)
Notice also that where the red diagonal line marked C' touches the tire is higher than where B touches the tire. This demonstrates that a consequence of turning is that the front-end of your motorcycle actually lowers based on rake geometry. The distance between where B and C (not C') touch the ground is called trail. (Trail, as you can see, is determined by rake angle, offset and tire radius.) Some motorcycles will have the hub of the front wheel either above or below the forks rather than directly in the middle of them. In effect, these placements are designed to reduce or increase the effect of the offset in order to increase or reduce trail.
The stability of your motorcycle at speed is a function of how long its trail is. However, have you ever noticed that the front wheel on bikes that have excessive rakes (and therefore long trail) have a tendency to flop over (at low speeds) when they are not aligned perfectly straight ahead? This is the phenomena that explains just one of the reasons why your wheel actually turns in the direction you want to go after it begins to lean in that direction. Any lean whatever of the wheel, because gravity tries to lower the front-end, receives an assist from gravity in its efforts to move the contact patch forward along the trail. Further, notice that the pivot axis of your forks is along C, not C' and that this is behind the bulk of the front-end. Thus, gravity plays an even bigger role in causing the wheel to turn than at first glance it would appear. (And now you see why you have steering dampers - so that a little lean doesn't result in a FAST tank-slapping fall of the wheel in the direction of the lean.)
But there is another, more powerful, reason that the lean is translated into a turn - Camber Thrust. Unlike automobile tires, your motorcycle rides on tires that are rounded instead of flat from side to side. When you are riding vertically your contact patch is right in the middle of the tire, at its farthest point from the hub of the wheel. When you are leaning you are riding on a part of the tire that is closer to the hub of the wheel. The farthest parts of the tire from the hub of the wheel are TURNING FASTER than any part closer to that hub. Thus, when you are leaning the outside edge of the contact patch is moving faster than is the inside edge.
Imagine taking two tapered drinking glasses and putting them together as in the next diagram. Does this not bear a striking resemblance to the profile of your tires when looking at them head on?
Now imagine placing one of those glasses on its side on the table and giving it a push. Note that the glass MUST move in a circle because the lip of the glass is moving faster than any other part of it. The same is true of your tires. This camber thrust forces your wheel to turn in response to a lean.
Thus, both the rake geometry and camber thrust conspire to cause a leaning front wheel to become a turn in the direction of the lean. Then, of course, the motorcycle body follows the wheel and it, too, leans in the direction of the turn.
So, now you know what counter-steering is, how it works, and why. What might just now be occurring to you is with all of these forces conspiring to cause the wheel to lean and then turn in the direction you want to go, what stops that wheel from going all the way to a stop every time a little counter-steer is used? And, as I earlier mentioned, how does a pilotless motorcycle automatically right itself?
The answer to both of those questions is centrifugal force and, again, rake geometry. For any given speed and lean combination there is only one diameter of a circle that can be maintained. This is a natural balance point at which gravity is trying to pull the bike down and centrifugal force is trying to stand it up, both with equal results. (If you have Excel on your system you might want to click on this link for a model that demonstrates this concept.)
If the speed is increased without a corresponding decrease in the diameter of the turn being made, centrifugal force will try to stand the bike more vertically - i.e., decreases the lean angle. This, in turn, decreases the camber thrust and the bike will, of its own accord, increase the diameter of the turn being made.
If the speed had been held constant but the bike attempts to shorten the diameter of the turn beyond that natural balance point then centrifugal forces are greater than gravity and it stands taller, again lengthening the diameter of the turn as described earlier.
Once your bike is stable in a curve (constant speed and constant lean) then it will stay that way until it receives some steering input. i.e., you again use some counter-steering or the road surface changes or the wind changes or you shift your weight in some way or you change speed.
As soon as any form of steering input occurs the stability of the bike is diminished. Momentum, camber forces and rake geometry will then engage in mortal combat with each other which will, eventually, cause the motorcycle to find a way to straighten itself out. That momentum will try to keep the motorcycle going in a straight line is obvious, but it also works with traction in an interesting way. That is, because the front tire's contact patch has traction the momentum of the entire motorcycle is applied to the task of trying to 'scrub' the rubber off that tire. If the body of the motorcycle is aligned with the front tire (only possible if traveling in a straight line) then there is essentially no 'scrubbing' going on. But if the bike is not in perfect alignment with the front tire, then momentum will try to straighten the wheel by pushing against the edge of that contact patch which is on the outside of the curve. As the contact patch touches the ground somewhere near point B, and because that is significantly behind the pivot axis of the front-end (red-dashed line C), the wheel is forced to pivot away from the curve.
I believe you now see why if the bike were to become pilotless it would wildly gyrate for a few moments as all of these conflicting forces battled each other and the bike became stable by seeking a straight path and being vertical. Clever, these motorcycle front-end designers. No?
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