Skid (automobile)

An automobile skid is an automobile handling condition where one or more tires are slipping relative to the road, and the overall handling of the vehicle has been affected.

Subtypes of skid include:

Tire slip, and related slip angle (angle of motion relative to tire), describe the performance of an individual tire. Important concepts here are circle of forces or circle of traction, and cornering force. To a first approximation, the tire can withstand approximately the same absolute force relative to the road surface in any direction. Graphically represented, a circle (or ellipse) of force magnitude represents the maximum tire traction, and the force vector can be in any direction up to the limit of the circle without tire slip. A tire that can withstand 0.8 G of force in braking can also withstand 0.8 G of force in turning or in acceleration, or for example approximately 0.56 G of cornering and 0.56 G of braking simultaneously, summing to 0.8 G at a 45 degree angle . Once the force exceeds the limit circle, that tire starts to slip.

Skidding is the vehicle's response to one or more tires slipping. The vehicle dynamics during a skid will depend on whether some or all of the tires are skidding, and whether the car was rotating or turning when the skid began.

Road surface conditions such as moisture on the road, snow, ice (particularly black ice), debris or sand, oil or other fluids, can cause skidding at much lower force levels or velocities than under normal conditions. Moisture can cause aquaplaning, better known as hydroplaning, where water builds up in front of and under tires and causes loss of tire grip.

Fishtailing is a cyclical skid combining alternating oversteer (rear wheel skidding) with overcorrection, leading to oversteer/skidding in the opposite direction.

Spin outs are where the vehicle starts to skid while rotating, or develops significant rotation while skidding, and rotates out of control.

Once the vehicle is rotating sufficiently rapidly, its angular momentum of rotation can overcome the stabilizing influence of the tires (either braking or skidding), and the rotation will continue even if the wheels are centered or past the point that the vehicle is controlled. This can be caused by some tires locking up in braking while others continue to rotate, or under acceleration where driven tires may lose traction (especially, if they lose traction unevenly), or in combining braking or acceleration with turning.

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Wikipedia