Skid Control

A basic guide can be defined as the loss of traction between a vehicle's tyres and the road surface due to the forces acting on the vehicle. Most skids are caused by driver error, although only about 15% of accidents are the direct result of a vehicle skidding. Skids occurring in other accidents are usually the result of last minute action, by the driver, when faced with a crisis ahead rather than actually causing an accident. Skids can occur both in the dry and wet as well as icy conditions, however, the chances of losing control and having an accident increase by 50% in the wet.

The main causes of skidding are as follows:

harsh or sudden acceleration
excessive of sudden braking
coarse or jerky steering movements

The effects of the above will be enhanced by speed. Combining these effects with non-recognition of adverse road and weather conditions will create problems for the driver.

The main types of skid that a driver could encounter on the public highway fall into three categories.

The front wheel skid.

The rear wheel skid.

The four wheel skid.

Preventive Measures

As well as the recognition of adverse road and weather conditions as a means of preventing skids from occurring, there are a number of other defensive actions that the driver can take.

Accelerate gently as opposed to harshly and in a straight line wherever possible.

Treat all braking operations in the same manner as acceleration.

If conditions are adverse, delicate use of foot controls and gentle shallow movements of the steering wheel are called for.

Ensure that the vehicle's position, speed and gear are correct before entering and negotiating the hazard.

Reduce speed in good time if conditions show any sign of deterioration.

Make sure the vehicle is correctly maintained, especially that tyre pressures are correct and the tyres are in good condition. Also have the vehicle's shock absorbers professionally checked; they are all that is holding you on the road.

If conditions look at all treacherous, allow extra time for the journey.

The Front Wheel Skid

Characteristics
The car tends to take a course outside of the expected course that the driver has steered (understeer); see figure 1.

Cause
Excess speed on entry to a hazard i.e. a corner or bend, or sudden braking to reduce the speed when negotiating the hazard. Both of these actions will have the effect of destabilising the vehicle making it more vulnerable to a loss of control.

Remedy
The inclination is to turn the steering wheel further to counteract the understeer. Should adhesion to the road surface be just within the limits, then adding a little more steering may be enough to counter the problem. If not, remove the cause by taking the right foot off the brake or accelerator pedal and fully depressing the clutch pedal, and if necessary reduce some of the steering; these actions should be simultaneous. The vehicle should now start regaining traction, but be prepared for the steering to 'snatch' when the vehicle gets back onto a less slippery surface. If the loss of control is exceptionally severe, then following the above action plus straightening the steering momentarily, to allow the front wheels to regain traction, and then steering gently back onto the original course will help to regain control.

The front wheel skid

The Rear Wheel Skid

Characteristics
The rear of vehicle swings out of line and gives the impression of trying to overtake the front (oversteer); see figure 2.

Cause
As with the front wheel skid, excessive speed into the hazard and sudden braking or acceleration with a rear wheel drive vehicle, destabilising the vehicle, are the main causes of this skid.

Remedy
Again take the right foot off the accelerator or brake and depress the clutch, then steer in the direction that the back of the vehicle is sliding (steer into the skid). Beware of correcting the steering too much as this may cause the vehicle to slide back in the opposite direction. As with the front wheel skid, these actions should be simultaneous, to prevent the back of the vehicle from building up too much momentum and sliding out of control.

The rear wheel skid

The Four Wheel Skid

Characteristics
All four wheels have locked up and the vehicle is sliding in the direction that the forward momentum is carrying it, with no directional control; see figure 3. It should be noted that both front and rear wheel skids, if unchecked sufficiently early, can develop into four wheel skids.

Cause
Harsh or sudden braking has caused the wheels to lock. A sensation of increase in the vehicle's speed often occurs.

Remedy
To achieve directional control, depress the clutch and rhythmically pump the brake pedal (cadence braking). This allows the brakes to lock and unlock. While they are unlocked, any movement of the steering wheel will have a positive effect. This is basically the same principle that ABS braking systems work on.

The four wheel skid

Why Follow These Actions?

In each case the cause can be removed by taking the foot off the accelerator or brake and depressing the clutch. The reasons are as follows:-

By decelerating, the vehicle's speed is lowered, which in turn will start to reduce the magnitude of the skid.

Relaxation of the pressure on the brake pedal will unlock the wheels and allow the tyres to regain traction, enabling the vehicle to be steered.

Depressing the clutch pedal has 3 beneficial effects:

The engine will not stall, enabling the vehicle to be moved quickly from the danger area.

The link between engine (providing power) and transmission is broken; there is no drive to any of the wheels, therefore the vehicle is no longer a front, rear or four wheel drive model.

A very slippery surface can cause the drive to lock up which in turn causes the wheels to lock, keeping the vehicle in a skid situation.

Skid Control

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