What Is All-Wheel Drive?
David Collins3-minute read
March 28, 2022
For most of automotive history, cars and trucks featured a drivetrain that delivered power to the two rear wheels by turning the rear axle. Vehicles that received power in all four wheels were rare and were mostly purpose-driven trucks that were used for towing, carrying heavy payloads, or tackling extreme terrain off-road. In the 21st century, the term all-wheel drive (AWD) has come to mean a different kind of four-wheel drive vehicle. The history of it dates back to the 1960s, with much of the early engineering focused on the Audi Quattro.
A vehicle that has all-wheel drive features a drivetrain that delivers power to all four wheels simultaneously, adjusting the amount of power in each wheel individually depending on driving conditions. On an icy or loose-gravel road, for instance, when one or more wheels loses traction, power is distributed differently to each wheel to maintain control of the vehicle. When driving conditions return to normal, power distribution is changed accordingly. Because of its versatility, all-wheel drive has become a huge selling point and has been developed for all kinds of vehicles, from compact cars to sedans to large SUVs. Today many vehicles feature AWD at least as an option, and on some it is standard.
Let’s dig in to learn more about how AWD works and how it’s different from 4-wheel drive.
How Does AWD Work?
All-wheel drive systems are governed by a computer that receives continuous input from sensors in the wheels. Some manufacturers differentiate between all-wheel drive systems that adjust continuously (full-time AWD) and those that engage only when driving conditions change (automatic AWD). In either case, adjustments take place without any driver input, which differentiates all-wheel drive from 4-wheel drive and 2-wheel drive.
For a quick primer on the major types of drivetrain, let’s define:
All-wheel drive (AWD): Power to all four wheels is variable, adjusts automatically without driver input.
4-wheel drive (4WD): Power to all four wheels, typically when engaged by driver input.
Front-wheel drive (FWD): Power only delivered to two front wheels.
Rear-wheel drive (RWD): Power only delivered to two rear wheels.
Limitations on all-wheel drive are that it is more expensive than a traditional 2-wheel drive configuration, and it gets slightly worse fuel economy. For venturing off the road, all-wheel drive is better than 2-wheel drive, but is less effective than most 4-wheel drive applications, as we’ll discuss below.
AWD Vs. 4WD
As all-wheel drive technology improves and is more in demand, the differences between all-wheel drive performance and traditional 4-wheel drive performance are shrinking. There are now trucks and large SUVs with all-wheel drive that handle deep snow and rugged terrain nearly as well as 4-wheel drive. There are also 4-wheel drivetrains that act like automatic AWD, switching without driver input from 2-wheel drive to 4-wheel power when conditions mandate.
The biggest difference between AWD and a traditional 4WD drivetrain is that all-wheel drive has a center differential that distributes power to all four wheels, while 4-wheel drive has independent front and rear differentials. Depending on how the vehicle’s 4-wheel drive is set up, both differentials can “lock” the axels for use in extremely difficult road conditions, which provides for more torque and thus better traction. Also, in a traditional 4-wheel drive vehicle, the driver decides when to shift from regular 2-wheel drive to 4-wheel drive, usually with a toggle switch on the dashboard. Some vehicles will also allow a shift to “4-Low” or “4-High,” with the lower gear reserved for use when extreme torque is required.
So, there are still differences between all-wheel drive and 4-wheel drive, and which is better depends on the needs of the driver. Generally, all-wheel drive is excellent for people who drive a car or SUV on mostly paved roads that will occasionally be icy or snow-covered. The AWD system quickly adjusts to fast-changing conditions and maintains vehicle control without the driver having to switch the system on. Four-wheel drive is great for delivering maximum torque at the driver’s request only, such as when linking up to tow a heavy boat or upon entering a rocky off-road trail.
It should be noted, however, that any AWD or 4WD vehicle can lose control if pushed into extreme snow or treacherous off-road terrain beyond its capability, and neither system improves stoppage time. Both systems improve towing capability, but before towing anything, drivers should know their vehicle’s towing capacity and not exceed that weight.
The Bottom Line: All-Wheel Drive Enhances Safety
The development of all-wheel drive has been hugely significant for automotive safety over the last few decades. Particularly for wet, icy, or snow-covered roads, an all-wheel drive car, SUV, or truck delivers better traction in all four wheels through continuous information-sharing between wheel censors and the vehicle’s computer. While most cars with an all-wheel drive option are also available in traditional 2-wheel drive, the extra expense for AWD is well worth it for drivers who encounter tricky winter driving surfaces.
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