Aquaplaning

This happens when there is water on the road and the car's speed is too great to allow the water to be channelled away by the tyre tread. Water builds up on the leading edge of the tyre and lifts the tread up so that there is less contact between the tyre and the road. If the speed of the car is sufficiently high the tyres are lifted completely off the road and steering control is completely lost:

A) Sinkage zone: water forms a wedge that lifts the tread - no contact

B) Transition zone - partial contact

C) Contact zone - the tread is in contact with the ground

There are four factors that determine whether an aquaplaning skid occurs:

• Depth of water. The more water there is, the more the tread has to channel away from the tyre.
• The contact shape of the tyre. That is the shape that is in contact with the ground. Wide tyres are more likely to skid than narrow ones as the car's weight is distributed over a greater surface area.
• The depth and shape of the tread on the tyre. The tread channels water away from the tyre and the shape determines how efficiently the tyre channels water. The deeper the tread the more water can be channelled. The tyres on racing cars are usually selected for the conditions - lucky race drivers!
• The speed of the car. If the speed is too great, water cannot be channelled fast enough from the tyre and water progressively builds up lifting the tyre off the road.

To regain control you need to do three things as soon as you recognize that you are skidding - immediately:

• Take your foot off the accelerator. This removes the power to the drive wheels.
• Steer gently so that when your speed has dropped to the point that the front wheels regain traction, the wheels are pointing in roughly the direction the car is moving.