Countersteering

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For the similar technique used in automobiles, see opposite lock.

Contents 1 How it works 1.1 Need to lean to turn 1.2 Lean by countersteering 1.3 Once lean is achieved 1.4 Adjusting or exiting a turn 1.5 At low speeds 1.6 Unconscious behavior 1.7 No hands 2 Motorcycles 3 See also 4 References 5 External links

Countersteering is the name given to the counter-intuitive technique used by cyclists and motorcyclists to turn corners. It is the only way a rider can cause the lean that a single-track vehicle must have in order to negotiate a turn successfully.

It is important to distinguish between countersteering as a physical phenomenon and countersteering as a rider technique for initiating a lean (the usual interpretation of the term). The physical phenomenon always occurs, because there is no other way to cause the bike and rider to lean short of some outside influence such as an opportune side wind, although at low speeds it can be lost or hidden in the minute corrections made to maintain balance.

At the same time, the rider technique of applying pressure to the handlebars to initiate a lean is not always necessary, since, on a sufficiently light bike (especially a bicycle), the rider can initiate a lean and so a turn by shifting body weight.^[1] Documented physical experimentation shows that on heavy bikes (many motorcycles) shifting body weight is ineffective at initiating leans and so turns.^[2]

It is also important to distinguish the momentary steering torque and steering angle necessary to initiate the lean required for a given turn from the sustained steering torque and steering angle necessary to maintain a constant radius and lean angle until it is time to exit the turn. The initial, momentary steer torque and angle are both opposite the desired turn direction. The sustained steer angle is in the same direction as the turn. The sustained steer torque required to maintain that steer angle is either with or opposite the turn direction depending on forward speed, bike geometry, and combined bike and rider mass distribution.

[edit] How it works

A single-track vehicle such as a bicycle or a motorcycle is an inverted pendulum -- it will fall over unless balanced. When a book is balanced on end, the bottom must be moved to the right to make the book fall to the left.

[edit] Need to lean to turn

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. Higher speeds and tighter turns require greater lean angles. If the mass is not first leaned into the turn, the momentum 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.^[3] The rider can shift his weight of course, but any force used to move one way laterally pushes the bike laterally the opposite direction with equal force. That makes the bike lean (and can affect the steering), but it doesn't lean the combined center of mass of bike and rider.

[edit] Lean by countersteering

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. Like the book example above, 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, if a rider wants to turn to the right, he 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.

[edit] Once lean is achieved

As the desired angle is approached, the rider must then steer 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. As roll momentum and gravity then tip the bike over to the side, the front wheel must be steered into the curve, and the curve is negotiated with the proper inward lean. 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.

[edit] Adjusting or exiting a turn

Once in a turn, countersteering is again required to make changes to its shape. The only way to decrease the radius at the same speed is to increase the lean angle, and the only way to increase the lean angle, is again to momentarily steer opposite to the direction of the curve. To the untrained, this can be extremely counter-intuitive.

To exit a turn, countersteer by momentarily steering further in the direction of the turn. This tilts the bike back upright.

[edit] 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 just noticeable difference or threshold of perception of the rider. Countersteering at low speed may be further concealed by the ensuing much large steering angle possible in the direction of the turn.

[edit] 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. Their bodies have learned to include the well timed countersteering jolt. They may have learned to do so while learning to ride a bicycle in childhood. Often people simply assume that the steering of a bike is just like the steering of a car. Their unconscious balance skills know better.

As is well-known in bicycle racing, the countersteering phenomenon becomes evident when there is an obstacle preventing the wheel from countersteering (e.g., when closely overlapping wheels or riding very close to a curb). In these situations, the only way to initiate a turn away from the obstacle is to come into contact with it, that is, turn towards the wheel or curb in order to avoid crashing into it.^[3] Lack of understanding of this principle leads to accidents in novice bicycle races.

[edit] No hands

This is how countersteering works when riding no-hands. In order to turn left, a rider applies a momentary torque, either at the seat via the legs or in the torso that causes the bike itself to lean to the right. The combined center of mass of the bike and rider is only lowered, of course. However, if the front of the bike is free to swivel about its steering axis, the lean to the right will cause it to steer to the right by some combination of gyroscopic precession, ground reaction forces, gravitational force on an off-axis center of mass, or simply the inertia of an off-axis center of mass, depending on the exact geometry and mass distribution of the particular bike, and the amount of torque and the speed at which it is applied.^[1][4]

This countersteering to the right causes the ground contact to move to the right of the center of mass, as the bike moves forward, thus generating a leftward lean. Finally the front end steers to the left and the bike enters the left turn. The amount of leftward steering necessary to balance the leftward lean appropriate for the forward speed and radius of the turn is controlled by the torque generated by the rider, again either at the seat or in the torso.

To straighten back out of the turn, the rider simply reverses the procedure for entering it: cause the bike to lean farther to the left; this causes it to steer farther to the left which moves the wheel contact patches farther to the left, eventually reducing the leftward lean and exiting the turn.

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. Riders may be able to keep a bike centered in a lane and negotiate shallow highway turns, but not much else.

[edit] Motorcycles

Even more so than on a bicycle, mastering the technique of countersteering is essential for safe motorcycle riding, and as a result is a part of the safe riding courses run by the Motorcycle Safety Foundation. At the higher speeds that motorcycles commonly attain, it becomes increasingly impractical to steer by taking advantage of the minute and random corrections needed to maintain balance.

Much of the art of motorcycle cornering is learning how to effectively "push" the grips into corners and how to maintain proper lean angles through the turn. When the need for a quick swerve to one side suddenly arises in an emergency, it is essential to know, through prior practice, that the handlebars must be deliberately pressed away on that side instead of being pulled. Many accidents result when otherwise experienced riders who have never carefully developed this skill encounter an unexpected obstacle.

[edit] See also

• Bicycle and motorcycle dynamics
• Motorcycle safety

[edit] References

[edit] External links

• Balance and Steering, by Tony Foale
• "Countersteering: Motorcycle Riders Who Zig"
• "Steering" (By Mike Howell)
• "No B.S. Machine" physical experimentation
• "Motorcycle Tire Wear" Inserted by and with permission of the author
• "Counter-Intuitive" (see Rocket Bike) relevant physical experimentation proving that turning bars to left cause bike to turn to the right