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 the transfer case. Transfer cases divide the transmission’s power, or torque, and sends it to both the front and rear driveshafts. The transfer case also locks the front and rear driveshafts together. This will force both the front and rear wheels to turn at the same speed. In an all-wheel drive vehicle, transfer cases actually allow the front and rear driveshafts to operate at different speeds. This will help the vehicle drive on any surface and make steering easier.Transfer cases also give your four-wheel drive vehicle an extra set of gears, which allow your vehicle to lower your transmission’s gear ratios into what is called a low-range. This will provide your vehicle with more torque, which will enable it to travel up steep hills and through snowy and muddy surfaces.