Hydroplaning (road vehicle)

From Free net encyclopedia

Hydroplaning (sometimes aquaplaning) in a road vehicle is an effect similar to planing in a boat. A layer of water between the rubber tires of a road vehicle and the road surface (or between airplane wheels and the runway) reduces the friction with the tires. They stop rotating, causing the vehicle to act like an unpowered and unsteered sled.

Causes of hydroplaning

The engine provides power through the wheels to provide a controlled speed. The wheels also provide steering and braking through the driver controlling the angle of the wheels relative to forward motion, and through the operation of the brakes. The tread in a rubber tire is designed to remove water from beneath the tire, providing high friction with the road surface even in wet conditions. This enables friction between the wheel and the road, allowing the wheel to rotate, and to provide rolling resistance, braking and steering power.

Wheeled vehicles are designed to operate properly when there is friction between the rotating wheel surface and the road. Any frictionless substance can force a vehicle to hydroplane, should the substance separate the tires from the road.

In a typical hydroplaning situation, increasing water pressure in front of the wheel means that the amount of water being dispersed by the tread is less than the amount being forced under the wheel. A wedge of water is forced under the tire which is lifted on a sheet of water.

The vehicle then loses braking, steering and power to the drive wheels because of loss of wheel contact with the road. The result is complete loss of normal control by the driver, and the vehicle will slide until it either collides with an obstacle or until wheel road friction is regained. The likelihood of hydroplaning increases if the momentum of the vehicle is high, the vehicle is imbalanced, the tire is underinflated, has worn tread or the water is deep.

Hydroplaning is especially dangerous while the car is on Cruise Control, as the increased reaction time and lack of pedal feel can cause the car to accelerate without warning. The problem with cruise control is that it may try to accelerate while the car has uneven traction. This can cause the vehicle to veer to the low traction side. The same problem can occur if the driver uses either gas or brake under uneven traction. When braking, the car will veer to the high traction side.

Two- or three-wheeled vehicles with round-profile tires, such as bicycles and motorcycles, virtually never suffer from hydroplaning in normal road use. The contact area with the road is a canoe-shaped patch which effectively squeezes water out of the way. Speeds of 200mph or more are necessary to achieve hydroplaning on narrow round-profile tires.

Loss of traction in low water situations

Hydroplaning occurs when there are large volumes of water on a road surface. Even slight wetness on a road can cause a car to lose traction. This effect, however, is different than what happens in hydroplaning.

Tires maintain traction on the road by using a mechanism called bulk friction, where the rubber of the tire pushes down into tiny pits in irregularities of the road surface. When a road becomes slightly wet, water can fill these pits such that the water tops them off without overflowing. As the narrow strip of tire that is in contact with the road rolls over these miniature puddles, the rubber of the tire seals the edges of the pits. By its nature, water can not be easily compressed, so each pit in essence then has a barrier over it preventing the rubber from pressing into it, thus reducing traction and leading to a reduction (but not necessarily complete loss) of control of the vehicle.

References

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