The Commercial Drivers License

SKID CONTROL AND RECOVERY

A skid happens whenever the tires lose their grip on the road.

This is caused in one of four ways:

• Overbraking. Braking too hard and locking up the wheels. Skids also can occur when using the speed retarder when the road is slippery.

• Oversteering. Turning the wheels more sharply than the vehicle can turn.

• Overacceleration. Supplying too much power to the drive wheels, causing them to spin.

• Driving too fast. Most serious skids result from driving too fast for road conditions. Drivers who adjust their driving to conditions don’t overaccelerate and don’t have to overbrake or oversteer from too much speed. Drive-Wheel Skids By far the most common skid is one in which the rear wheels lose traction through excessive braking or acceleration. Skids caused by acceleration usually happen on ice or snow. They can be easily stopped by taking your foot off the accelerator. (If it is very slippery, push the clutch in. Otherwise the engine can keep the wheels from rolling freely and regaining traction.) Rear wheel braking skids occur when the rear drive wheels lock. Because locked wheels have less traction than rolling wheels, the rear wheels usually slide sideways in an attempt to “catch up” with the front wheels. In a bus or straight truck, the vehicle will slide sideways in a “spin out.” With vehicles towing trailers, a drive-wheel skid can let the trailer push the towing vehicle sideways, causing a sudden jackknife. (Figure 2-14)

Correcting a Drive-Wheel Braking Skid

Do the following to correct a drive-wheel braking skid:

• Stop braking. This will let the rear wheels roll again, and keep the rear wheels from sliding any further. If on ice, push in the clutch to let the wheels turn freely.

• Turn quickly. When a vehicle begins to slide sideways, quickly steer in the direction you want the vehicle to go—down the road. You must turn the wheel quickly. • Countersteer. As a vehicle turns back on course, it has a tendency to keep right on turning. Unless you turn the steering wheel quickly the other way, you may find yourself skidding in the opposite direction.

Learning to stay off the brake, turn the steering wheel quickly, push in the clutch, and counter-steer in a skid takes a lot of practice. The best place to get this practice is on a large driving range or “skid pad.”

Front-Wheel Skids

Most front-wheel skids are caused by driving too fast for conditions. Other causes are: lack of tread on the front tires, and cargo loaded so not enough weight is on the front axle. In a front-wheel skid, the front end tends to go in a straight line regardless of how much you turn the steering wheel. On a very slippery surface, you may not be able to steer around a curve or turn. When a front-wheel skid occurs, the only way to stop the skid is to let the vehicle slow down. Stop turning and/or braking so hard. Slow down as quickly as possible without skidding.