CDL: Skidding
Skid Control and Recovery: What Causes Skids and How to Correct Them
A skid is one of the most unnerving things that can happen behind the wheel of a commercial vehicle — but it isn't random bad luck. Skids have specific causes, and once you understand them, you can both avoid triggering one and react correctly if one happens anyway. This article covers why skids occur, how to handle the most common type, and what to do when the front of the vehicle loses its grip.
What Causes a Skid?
A skid happens any time the tires lose their grip on the road surface. There are four main ways this can happen:
- Overbraking: Braking too hard and locking up the wheels. Using a speed retarder on a slippery road can trigger the same kind of skid.
- Oversteering: Turning the wheels more sharply than the vehicle is capable of handling.
- Overacceleration: Sending too much power to the drive wheels, causing them to spin.
- Driving too fast: Most serious skids ultimately come down to speed. Drivers who adjust their speed to match road conditions rarely find themselves needing to brake, steer, or accelerate hard enough to trigger a skid in the first place.
Drive-Wheel Skids
The most common type of skid by far occurs when the rear wheels lose traction, usually from either excessive braking or excessive acceleration.
Skids caused by acceleration tend to happen on ice or snow, and they're usually easy to correct — simply taking your foot off the accelerator is often enough to stop them. If conditions are especially slippery, pushing in the clutch can help, since it lets the wheels roll freely and regain traction rather than having the engine continue to fight against them.
Skids caused by braking happen when the rear drive wheels lock up. Because a locked wheel actually has less traction than a wheel that's still rolling, the rear of the vehicle tends to slide sideways as it tries to "catch up" with the front. In a bus or straight truck, this shows up as the whole vehicle sliding sideways in what's sometimes called a spin-out. In a vehicle towing a trailer, the same kind of skid can cause the trailer to push the towing vehicle sideways, resulting in a sudden jackknife.
Correcting a Drive-Wheel Braking Skid
Stop braking. Releasing the brakes lets the rear wheels start rolling again, which stops them from sliding any further. On ice, pushing in the clutch lets the wheels roll freely as well.
Turn quickly. Once the vehicle begins sliding sideways, steer promptly in the direction you want the vehicle to travel — straight down the road. This has to be done quickly to be effective.
Countersteer. As the vehicle straightens back onto its course, it will tend to keep turning past where you want it to stop. Unless you quickly turn the wheel back the other way, you risk skidding in the opposite direction instead. Learning to stay off the brake, turn the wheel quickly, push in the clutch, and countersteer all takes real practice — ideally on a large, open driving range or "skid pad" designed for exactly this kind of training.
Front-Wheel Skids
Front-wheel skids are most often the result of driving too fast for the conditions, though a lack of tread on the front tires or cargo loaded in a way that leaves too little weight on the front axle can also contribute. In this kind of skid, the front of the vehicle simply continues traveling in a straight line no matter how much the steering wheel is turned. On a very slippery surface, this can mean you're unable to steer around a curve or turn at all.
Unlike a drive-wheel skid, a front-wheel skid can't be corrected through steering. The only way to stop it is to let the vehicle slow down — ease off the turn and off the brake, and reduce speed as quickly as you safely can without triggering a different kind of skid in the process.
Skids are rarely a matter of chance — they're the predictable result of overbraking, oversteering, overaccelerating, or simply carrying too much speed into a situation the road can't support. Understanding both what causes each type of skid and how to respond gives you a real chance of recovering control rather than making the situation worse.