Ask a Technician: What Are the Differences Between Rear-Wheel Drive, Front-Wheel Drive, 4WD, and AWD?
The differences between front-wheel drive and rear-wheel drive are well established, but not so the differences between all-wheel-drive (AWD) and four-wheel-drive (4WD), as many automakers tend to muddy thew waters. So here’s Germain Toyota of Columbus's quick rundown on which drivetrain is which.
Front-wheel drive is relatively simple, as the engine is usually mounted across the nose of the car (transverse mounted). This allows the drive shafts to transmit power directly to the front wheels, which are obviously also the wheels that steer. Front-wheel drive is attractive to automakers as it creates more room inside the car (due to the lack of a transmission tunnel) and also is usually cheaper because fewer components are required. Front-wheel drive is also handy in slippery road conditions, as the weight of the engine presses down on the front tires to make them grip better.
Rear-wheel drive is usually built around an engine that is mounted in line with the car (longitudinal mounted), and the rear wheels are connected to the engine through a driveshaft that runs the length of the car. The advantages to rear-wheel drive are better steering response, and the ability to spread the loads of a car across all four tires (while front-wheel drive cars have to handle the tasks of both steering and pulling the car at the same time.)
Many car makers have 4WD systems that are not four-wheel drive all the time, but can be used in low-traction situations to send power to the front or rear wheels (whichever are not being used at the time). Part-time 4WDs typically have a locking transfer case that activates when the system is engaged. This then locks the front and rear wheel differentials together so the same amount of power is sent to them. This sort of four-wheel drive system cannot be used on road, because the result is transmission windup when all four tires are trying to rotate at the same speed.
AWD is most often used to describe a system where all the wheels have power sent to them all the time. This involves an extra differential between the front and rear wheels so that variable amounts of power can be sent to the wheels. If you didn’t have a center differential the power sent to the front and rear wheels force the wheels to rotate at the same speed and put pressure on the transmission system (also called transmission windup).
To summarize, front-wheel drive is popular because it allows extra space inside the vehicle and good traction in slippery conditions, while rear-wheel drive allows greater power outputs and better steering. AWD is a user friendly system that ensures that all wheels are driven all the time for best traction, part-time 4WD is an automatic system that activates power to all wheels when required, and full-time 4WD (along with some AWD systems) is used mostly for vehicles that regularly drive off-road.