Skidding is defined as the involuntary movement of the vehicle due to the grip of the tyre on the road becoming less than the force or forces acting on the vehicle. In other words a vehicle skids when one or more of the tyres lose their normal grip on the road.

The forces being applied to a vehicle will include acceleration, deceleration (usually braking) and side ways forces created by the driver whilst negotiating a corner or bend. The other key force is that of gravity and the resultant forces being placed upon the vehicle and the current road and weather conditions.

The main causes of skidding, either singly or in combination are;-

1. Excessive speed for the existing circumstances – this is a basic cause.
2. Coarse steering in relation to speed which is not in itself excessive, OR banking a solo too far over when turning a corner.
3. Harsh acceleration.
4. Excessive or sudden braking.

Recognition & correction of skids
It is essential that each type of skid is recognised in the early stages of development if corrective measures are to be taken.

Rear wheel skid
This occurs when the rear wheels lose their grip on the road and the vehicle may swing in either direction. It can be caused by all four causes above and if unchecked can cause the vehicle to broadside or completely turn around.

To eliminate the causes relaxing pressure on the accelerator or brake pedal at the same time applying some steering in the direction of the skid, i.e. if the vehicle is skidding to the left, turn the steering wheel to the left. When stability has been regained the vehicle can be returned to the desired course. Care should be taken not to over steer as a further skid may be induced.

Front wheel skid
This usually occurs when cornering or on a bend when the front wheels lose their grip and the vehicle does not travel in the direction in which it is being steered. It can be caused by 1 – 3 above and in the case of a front wheel drive vehicle 4.

To eliminate the cause by relaxing the accelerator or brakes momentarily straighten the steering to allow the front wheels to regain their grip and then gently steer to course. The driver should be prepared for the sudden grip of the front wheels as deceleration becomes effective.

Four wheel skid
This occurs when all wheels lose their grip on the road. It is usually associated with Excessive or sudden braking. The effects may be a combination of both front and rear wheel skidding. On a wet or slippery roads maximum deceleration may be gained by cadence braking. It should be remembered that a four wheel skid may also be a progression from a front or rear wheel skid which may not be corrected.

Minimise the risk of skidding

1. Vary the speed of your vehicle according to the road and weather conditions.
2. Use good observation and change driving plans accordingly.
3. Recognise changes in road surface conditions, e.g. mud, snow, rain, loose surface, i.e. gravel or road debris, etc.
4. Ensure tyres have adequate tread depth and are properly inflated
5. Vary braking and acceleration according to the conditions.
6. Concentrate at all times to avoid a kid from developing.

General
If a skid is allowed to develop a driver will rarely find that they have sufficient time or space to correct it. Concentration and good observation are essential if skids are to be avoided and quick reactions are necessary when a skid develops.

It is important again to stress that on a very slippery road the best control is through the accelerator with a suitable gear engaged.

The reduction of speed on a slippery surface is best done through acceleration sense and the use of engaging a lower gear but it is important to do this as smoothly as possible.

Skidding must not be practiced on public roads – there are many companies that provide skid training facilities and these should be used to practice your immediate action should a skid occur.

Stewart Rivers Chief Observer NET RoADA

Stewart Rivers is a Superintendent with the Metropolitan Police and their most senior practicing Class 1 driver