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Difference between revisions of "Counter steering"
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A single-track vehicle such as a bicycle or a motorcycle is an inverted pendulum—it will fall over unless balanced. | A single-track vehicle such as a bicycle or a motorcycle is an inverted pendulum—it will fall over unless balanced. | ||
The technique used by cyclists and [[Motorcycling|motorcyclists]] to initiate turning in a given direction is to first apply a steering torque in the opposite direction. For example, if a turn to the left is desired, it is started by a turn of the handlebars to the right. Under this force the front wheel will rotate to turn right and the front tire will generate forces to the right. The machine as a whole steers to the right briefly and the rear tire also generates forces to the right. Because the forces are applied at ground level, this pulls the wheels "out from under" the motorcycle and to its right. The resulting roll angle to the left causes the tires to then generate camber thrust to the left providing the | The technique used by cyclists and [[Motorcycling|motorcyclists]] to initiate turning in a given direction is to first apply a steering torque in the opposite direction. For example, if a turn to the left is desired, it is started by a turn of the handlebars to the right. Under this force the front wheel will rotate to turn right and the front tire will generate forces to the right. The machine as a whole steers to the right briefly and the rear tire also generates forces to the right. Because the forces are applied at ground level, this pulls the wheels "out from under" the motorcycle and to its right. The resulting roll angle to the left causes the tires to then generate camber thrust to the left providing the centripetal forces required to turn left. The geometry of the steering system provides the forces necessary for the front wheel to adopt an angle turned into the turn in a conventional manner<ref>{{cite web | ||
| url = http://www.phys.lsu.edu/faculty/gonzalez/Teaching/Phys7221/vol59no9p51_56.pdf | | url = http://www.phys.lsu.edu/faculty/gonzalez/Teaching/Phys7221/vol59no9p51_56.pdf | ||
| first = David | | first = David | ||
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It is often claimed that two-wheeled vehicles can be steered using only weight shifts. While this is true for small "trim" inputs to direction, complex maneuvers are not possible using weightshifting alone because even for a light machine there is insufficient control authority.<ref name="evangelou">Evangelou, S, 2004 "The Control and Stability Analysis of Two-Wheeled Road Vehicles", PhD Thesis, Imperial College London</ref> | It is often claimed that two-wheeled vehicles can be steered using only weight shifts. While this is true for small "trim" inputs to direction, complex maneuvers are not possible using weightshifting alone because even for a light machine there is insufficient control authority.<ref name="evangelou">Evangelou, S, 2004 "The Control and Stability Analysis of Two-Wheeled Road Vehicles", PhD Thesis, Imperial College London</ref> | ||
Although on a sufficiently light bike (especially a | Although on a sufficiently light bike (especially a bicycle), the rider can initiate a lean and turn by shifting body weight,<ref name="fajans"/>, there is no evidence that complex maneuvers can be performed by bodyweight alone | ||
<ref name="code"/>. | <ref name="code"/>. | ||
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===Need to lean to turn=== | ===Need to lean to turn=== | ||
A bike can negotiate a curve only when the combined | A bike can negotiate a curve only when the combined center of mass of bike and rider leans toward the inside of the turn at an angle appropriate for the velocity and the radius of the turn: | ||
:<math>\theta = \arctan \left (\frac{v^2}{gr}\right )</math> | :<math>\theta = \arctan \left (\frac{v^2}{gr}\right )</math> | ||
where <math>v</math> is the forward speed, <math>r</math> is the radius of the turn and <math>g</math> is the acceleration of | where <math>v</math> is the forward speed, <math>r</math> is the radius of the turn and <math>g</math> is the acceleration of gravity.<ref name="fajans" /> | ||
Higher speeds and tighter turns require greater lean angles. If the mass is not first leaned into the turn, the | Higher speeds and tighter turns require greater lean angles. If the mass is not first leaned into the turn, the inertia of the rider and bike will cause them to continue in a straight line as the tires track out from under them along the curve. The transition of riding in a straight line to negotiating a turn is a process of leaning the bike into the turn, and the only way to cause that lean (of the combined center of mass of bike and rider) is to move the support points in the opposite direction first.<ref name="Wilson">{{cite book | ||
| title = Bicycling Science | | title = Bicycling Science | ||
| edition = Third | | edition = Third | ||
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When riding a bicycle or a motorcycle, countersteering is a method of initiating a turn by a small, momentary turn of the front wheel, usually via the handlebars, in the opposite (counter) direction. This moves the pivot point (the wheels' contact patches) out from under the center of mass to establish the lean angle for a turn. While necessary at all speeds, the need to countersteer becomes more noticeable as speed increases. | When riding a bicycle or a motorcycle, countersteering is a method of initiating a turn by a small, momentary turn of the front wheel, usually via the handlebars, in the opposite (counter) direction. This moves the pivot point (the wheels' contact patches) out from under the center of mass to establish the lean angle for a turn. While necessary at all speeds, the need to countersteer becomes more noticeable as speed increases. | ||
Hence, to turn to the right, the rider first throws the bike off balance by momentarily pointing the front wheel slightly to the left. The center of mass of the bike plus rider will continue in a straight line, but the | Hence, to turn to the right, the rider first throws the bike off balance by momentarily pointing the front wheel slightly to the left. The center of mass of the bike plus rider will continue in a straight line, but the contact patches of the tires move to the left with respect to this straight line. | ||
===Once lean is achieved=== | ===Once lean is achieved=== | ||
As the desired angle is approached, the front wheel must then be steered into the turn to maintain that angle or the bike will continue to lean with gravity, increasing in rate, until the side contacts the ground. This process usually requires little physical effort, because the | As the desired angle is approached, the front wheel must then be steered into the turn to maintain that angle or the bike will continue to lean with gravity, increasing in rate, until the side contacts the ground. This process usually requires little physical effort, because the geometry of the steering system of most bikes is designed in such a way that the front wheel has a strong tendency to steer in the direction of a lean. | ||
The actual torque the rider must apply to the handlebars to maintain a steady-state turn is a complex function of bike geometry, mass distribution, rider position, turn radius, and forward speed. At low speeds, the steering torque necessary from the rider is usually negative, that is opposite the direction of the turn, even when the steering angle is in the direction of the turn. At higher speeds, the direction of the necessary input torque often becomes positive, that is in the same direction as the turn.<ref name="Cossalter">{{cite book | The actual torque the rider must apply to the handlebars to maintain a steady-state turn is a complex function of bike geometry, mass distribution, rider position, turn radius, and forward speed. At low speeds, the steering torque necessary from the rider is usually negative, that is opposite the direction of the turn, even when the steering angle is in the direction of the turn. At higher speeds, the direction of the necessary input torque often becomes positive, that is in the same direction as the turn.<ref name="Cossalter">{{cite book | ||
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===At low speeds=== | ===At low speeds=== | ||
At low speeds countersteering is equally necessary, but the countersteering is then so subtle that it is hidden by the continuous corrections that are made in balancing the bike, often falling below a | At low speeds countersteering is equally necessary, but the countersteering is then so subtle that it is hidden by the continuous corrections that are made in balancing the bike, often falling below a just noticeable difference or threshold of perception of the rider. Countersteering at low speed may be further concealed by the ensuing much larger steering angle possible in the direction of the turn. | ||
===Unconscious behavior=== | ===Unconscious behavior=== | ||
Countersteering is indispensable for bike steering. Most people are not consciously aware that they employ countersteering when riding their bike any more than they are aware of the physics of walking. They have learned to subsconciously apply the required countersteering. | Countersteering is indispensable for bike steering. Most people are not consciously aware that they employ countersteering when riding their bike any more than they are aware of the physics of walking. They have learned to subsconciously apply the required countersteering. | ||
===Gyroscopic effects=== | ===Gyroscopic effects=== | ||
One effect of turning the front wheel is a roll | One effect of turning the front wheel is a roll moment caused by gyroscopic precession. The magnitude of this moment is proportional to the moment of inertia of the front wheel, its spin rate (forward motion), the rate that the rider turns the front wheel by applying a torque to the handlebars, and the cosine of the angle between the steering axis and the vertical.<ref name="Cossalter"/> | ||
For a sample motorcycle moving at 22 m/s (50 mph) that has a front wheel with a moment of inertia of 0.6 kgm<sup>2</sup>, turning the front wheel one degree in half a second generates a roll moment of 3.5 Nm. In comparison, the lateral force on the front tire as it tracks out from under the motorcycle reaches a maximum of 50 N. This, acting on the 0.6 m (2 ft) height of the center of mass, generates a roll moment of 30 Nm.<ref name="Cossalter"/> | For a sample motorcycle moving at 22 m/s (50 mph) that has a front wheel with a moment of inertia of 0.6 kgm<sup>2</sup>, turning the front wheel one degree in half a second generates a roll moment of 3.5 Nm. In comparison, the lateral force on the front tire as it tracks out from under the motorcycle reaches a maximum of 50 N. This, acting on the 0.6 m (2 ft) height of the center of mass, generates a roll moment of 30 Nm.<ref name="Cossalter"/> | ||
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The reason this no-hands steering is less effective on heavy bikes, such as motorcycles, is that the rider weighs so much less than the bike that leaning the torso with respect to the bike does not cause the bike to lean far enough to generate anything but the shallowest turns. No-hands riders may be able to keep a heavy bike centered in a lane and negotiate shallow highway turns, but not much else. | The reason this no-hands steering is less effective on heavy bikes, such as motorcycles, is that the rider weighs so much less than the bike that leaning the torso with respect to the bike does not cause the bike to lean far enough to generate anything but the shallowest turns. No-hands riders may be able to keep a heavy bike centered in a lane and negotiate shallow highway turns, but not much else. | ||
==Motorcycles== | ==Motorcycles== | ||
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| accessdate = 2009-12-31}}</ref> and is summed up in a simplified way as "Push the right-hand bar to steer right; push the left-hand bar to steer left". | | accessdate = 2009-12-31}}</ref> and is summed up in a simplified way as "Push the right-hand bar to steer right; push the left-hand bar to steer left". | ||
==The Wright Brothers== | ==The Wright Brothers== | ||
Wilbur Wright explains countersteering this way: | |||
{{Quote| | {{Quote| | ||
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==External links== | ==External links== | ||
*[http://www.tonyfoale.com/Articles/Balance/BALANCE.htm Balance and Steering], by | *[http://www.tonyfoale.com/Articles/Balance/BALANCE.htm Balance and Steering], by Tony Foale | ||
*[http://www.superbikeschool.com/machinery/no-bs-machine.php "No B.S. Machine"] physical experimentation | *[http://www.superbikeschool.com/machinery/no-bs-machine.php "No B.S. Machine"] physical experimentation | ||
[[Category:Motorcycle riding techniques]] | [[Category:Motorcycle riding techniques]] | ||
[[Category:Motorcycle | [[Category:Motorcycle physics]] | ||
[[Category:Motorcycles]] | |||
[[Category:Mopeds]] | [[Category:Mopeds]] | ||