When riding a bicycle or a motorcycle, countersteering is a method of preparing for a turn by a small, momentary turn of the handlebars in the opposite direction. The necessity to countersteer becomes noticable above a minimum speed.
A bike can negotiate a curve only when it leans towards the inside of the turn, at a camber angle appropriate for the velocity and the sharpness of the turn. At higher velocities, the bike has a strong natural tendency to remain upright. The transition of riding in a straight line to negotiating a turn is a process of shifting the balance of the bike. In a sense, the bike needs to be thrown off balance first.
If a biker wants to turn to the right, he first throws the bike off balance by a well-timed jolt to the handlebars, 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. As the bike is being tipped over to the right the front wheel is steered into the curve, and the curve is negotiated with the proper inward lean. This proces requires little physical effort, because the geometry of the steering of a bike is designed in such a way that the front wheel has a strong tendency to follow the balance of the bike.
When a bike in a standstill position is standing upright, the weight of the bike is pointing the front wheel forward. Turning the handlebars in this situation raises the bike slightly, if the handlebars are released the weight of the bike tends to return the front wheel to a forward direction. When a bike in a standstill position is tipped over, the front wheel finds itself a new equilibrium position that is turned toward the directon the bike is tipped over. When a bike at speed is pulling G's the artificial G's tend to straighten the front wheel, again assisting the steering of the bike.
At low speeds countersteering is equally necessary, but the countersteering is so subtle then that it drowns in the continuous corrections that are made in balancing the bike.
Contrary to what one might expect, above a minimum velocity a bicycle can be ridden "handsfree" with great accuracy. All the steering is then done by shifts of balance, as the front wheel tends to follow the balance.
Countersteering is indispensible for bicycle steering. Most people are not consciously aware that they employ countersteering when riding their bicycle. Their body has learned to include the well timed countersteering jolt, they have learned to do so while learning to ride a bicycle in childhood. Often people simply assume that the steering of a bicycle is just like the steering of a car. Their subconscious balance skills know better: they shift their balance first, and then the front wheel tends to steer into the turn that the rider has in mind.
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