Vehicles such as cars, trucks, SUVs and vans have different drive assemblies that their engines use to transmit power to the wheels and move them along the road. The two main types of assemblies are 2-wheel drive and 4-wheel drive. This refers to the number of wheels driven by the engine via the driveline that provide the vehicle with motion. In a vehicle with four wheels, such as an auto, 2-wheel drive is often used because of its simplicity and the amount of traction provided by the road. When you buy a vehicle and see the abbreviation 2WD, you need to understand exactly what it means and how it applies to the performance of your vehicle.
2-wheel drive vehicles typically come in two types: front-wheel drive (FWD) and rear-wheel drive (RWD). A typical small car such as a small sedan will feature front-wheel drive. Cars with FWD tend to be lighter. In a front-wheel-drive vehicle, the drivetrain that transmits the engine force to the wheels can be shorter. This means less overall weight and better fuel economy -- an important factor in today's era of skyrocketing fuel prices. FWD makes a car prone to understeering, that is, it pushes in a straighter line when cornering compared to the orientation of the tires. This is due to the forward weight distribution.
Rear-wheel drive cars have their own advantages. They distribute the weight of the car more evenly and allow for easier turning under normal conditions -- front-wheel drive cars tend to have more traction on slick surfaces because of the increased weight on the driven wheels. Rear-wheel drive allows for more acceleration from a stop as weight shifts to the rear due to inertia and presses the rear tires against the road.
Two-wheel-drive vehicles have been in existence since cars became commonplace, because of the relative low cost of drivetrains and other components. In all-wheel-drive or 4-wheel-drive vehicles, multiple drivetrains have to be used to balance weight and force equally across all four tires. Most all-terrain vehicles use some sort of all-wheel-drive system to maximize traction on virtually any driving surface.
Choosing the layout of your new vehicle is important for your safety and for your sense of controlling the car when you drive. Because most road vehicles feature 2-wheel drive, your main choice is going to be between FWD and RWD. Modern vehicles have electronic traction controls and sensors that adjust based on road conditions and balance out the disadvantages of each, but you will likely notice a difference in how the vehicle handles. Take the car for a test drive before you consider purchasing it to get a feel for how it works, especially if the drive type is unfamiliar to you.