Answer: Simply put, four-wheel drive means that your vehicle is supplying power to all four wheels. Four-wheel drive systems are designed to give your vehicle better traction on snow and ice and in off-road conditions. The majority of four-wheel drive vehicles are only part-time four-wheel drive vehicles. This means that the vehicle’s four-wheel drive system can be turned on or off. Another type of four-wheel drive vehicle is an all-wheel drive vehicle. This means that the vehicle is always in four-wheel drive and is made to drive in any condition, such as ice, snow, and off-road. Whether you have an all-wheel drive or a part-time four-wheel drive vehicle, your four-wheel drive system is designed to send a precise amount of torque to each wheel to prevent each wheel from slipping.To get a better understanding of how four-wheel drive systems work, it is important to understand a little bit more about torque and wheel slip. Torque is a force used to turn things. In this case, torque is produced by your engine and is used to turn your vehicle’s wheels. Now, in bad weather conditions, your vehicle’s torque is actually determined by traction, not your engine. More specifically, it is determined by the amount of traction your tires have on the road surface. Wheel slip is all about your wheels contact with the road surface and whether your wheels have good traction or bad traction. Basically, when your wheel’s torque is greater than its traction, it experiences wheel slip. So, what four-wheel drive systems do is offer a greater amount of possible torque to your wheels but also supply the right amount of torque to sustain good traction in poor conditions. Four-wheel drive vehicles also provide better traction to all four wheels, which in turn increases the amount of torque, or force, that your tires can receive. This in turn will help your vehicle travel through snow and up slippery hills more efficiently. There are many parts in four-wheel drive systems that make four-wheel drive vehicles possible. One such part is locking hubs. Locking hubs are located on the front wheels of part-time four-wheel drive vehicles. Locking hubs are used to lock, or engage, the two front wheels so they also become drive wheels. This will put your vehicle into four-wheel drive. They are also used to disengage the front wheels from the front differential or drive shaft, setting the vehicle back into two-wheel drive. This allows the front differential or drive shaft to stop spinning, which will decrease the amount of friction applied to all the parts in the front differential, extending their life, improving fuel economy, and also preventing excessive wear on the front tires.