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
• 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.”
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.