4 x 4

4 x 4 Information

There are almost as many different types of four-wheel-drive systems as there 4 x 4 vehicles. It seems that every manufacturer has several different schemes for providing power to all of the wheels. The language used by the different carmakers can sometimes be a little confusing, so before we get started explaining how they work, let's clear up some terminology:

  • Four-wheel drive - Usually, when carmakers say that a car has four-wheel drive, they are referring to a part-time system. For reasons we'll explore later in this article, these systems are meant only for use in low-traction conditions, such as off-road or on snow or ice.
  • All-wheel drive - These systems are sometimes called full-time four-wheel drive. All-wheel-drive systems are designed to function on all types of surfaces, both on- and off-road, and most of them cannot be switched off.

Part-time and full-time 4x4 systems can be evaluated using the same criteria. The best system will send exactly the right amount of torque to each wheel, which is the maximum torque that won't cause that tire to slip.

This can help in a variety of situations. For instance:-

  • In snow - It takes a lot of force to push a car through the snow. The amount of force available is limited by the available traction. Most two-wheel-drive cars can't move if there is more than a few inches of snow on the road, because in the snow, each tire has only a small amount of traction. A 4x4 car can utilize the traction of all four tires.
  • Off road - In off-road conditions, it is fairly common for at least one set of tires to be in a low-traction situation, such as when crossing a stream or mud puddle. With four-wheel drive, the other set of tires still has traction, so they can pull you out.
  • Climbing slippery hills - This task requires a lot of traction. A 4x4 car can utilize the traction of all four tires to pull the car up the hill.

There are also some situations in which four-wheel drive provides no advantage over two-wheel drive. Most notably 4x4 systems won't help you stop on slippery surfaces. It's all up to the brakes and the anti-lock braking system (ABS).

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