AWD vs. 4WD: What's the Difference?

If you find yourself asking what the difference between four-wheel drive and all-wheel drive is, don't feel bad. It can get confusing. What it boils down to is whether or not the vehicle has a multi-speed transfer case. A transfer case is effectively a second gearbox, usually mounted behind the transmission, that allows drivers to select a mechanically lower gear, which aids off-road driving by multiplying torque and increasing control on ascents and descents.

Most all-wheel-drive vehicles won’t have a selectable low range, but many four-wheel-drive vehicles use what’s known as "full-time" four-wheel drive. This means they always drive all four wheels while still having a selectable low range. Other four-wheel-drive vehicles will spend most of their time in two-wheel drive and require the operator to select four-wheel drive manually. This approach was the most common design for many years and is still in use today in many trucks.

Some all-wheel-drive vehicles can also choose to drive either just the front or rear wheels, depending on how the vehicle was engineered. But many, like Subarus, will constantly drive all four wheels, adjusting the bias of engine torque sent to each axle to suit road conditions.

Jump to:

• How does all-wheel drive work?
• Full-time AWD
• Part-time AWD
• What are the disadvantages of AWD?
• How does four-wheel drive work?
• Full-time 4WD
• Part-time 4WD
• AWD vs. 4WD: Which is best?

How does all-wheel drive work?

Both full-time and part-time systems generally operate with no input from the driver, although some offer selectable modes that allow a limited amount of control over how much power goes where. All the wheels get torque through a series of differentials, viscous couplings and/or multiplate clutches, which help distribute power to the wheels in such a way that the wheel with traction gets the torque. Many all-wheel-drive traction systems employ the brakes to aid torque distribution.

Full-time AWD

In full-time AWD, both the front and rear axles are driven all the time. On dry pavement, this kind of AWD can help the vehicle handle better and ensure that full power gets to the road. And in slippery conditions, such as ice, snow or mud, it provides always-ready traction for safer, more confident handling. Historically, a good example of full-time AWD was Audi's Quattro system, but Subaru's Symmetrical All-Wheel Drive deserves some accolades.

Part-time AWD

In normal operation, part-time AWD sends torque to two driven wheels, either the front or rear depending on the vehicle. The part-time system then automatically engages the other wheels when road conditions demand extra traction. Modern part-time AWD uses an array of electronic sensors that feed information to a computer, which controls the amount of power directed to each wheel. This setup is commonly found on car-based crossover SUVs and AWD cars. Increasingly, hybrid vehicles with AWD use the internal combustion engine to power one axle and an electric motor to power the other. A good example of this is the current Lexus RX SUV.

What are the disadvantages of AWD?

While AWD works well in a variety of conditions, from rain and snow to light off-roading, most systems are simply not robust enough to handle rough, uneven and slippery terrain. That means you're limited in how far you can venture into the muck without possibly getting stuck. While that AWD hatchback may seem hardy enough to get you to a distant campsite, you'll need to exercise caution, lest you find yourself calling for a pricey off-road tow.

How does four-wheel drive work?

Like AWD systems, 4WD is designed to maximize traction front and rear. But 4WD systems tend to be more robust than AWD ones and can generally handle more rugged terrain. And they, too, come in two types: full-time and part-time.

Traditional 4WD systems have a two-speed transfer case with high- and low-range modes that can be selected by the driver, either with an electronic switch or a mechanical lever. The low-range setting multiplies torque to provide superior control and grunt in low-speed off-road environments, such as climbing rocks or powering through deep mud. The high-range setting is useful for less challenging off-road scenarios as well as slippery on-road conditions, such as packed snow, ice, loose sand and gravel.

Full-time 4WD

Full-time 4WD operates as a full-time AWD system does, with all four wheels receiving power on a continuous basis. Late-model Toyota Land Cruisers and Land Rovers are good examples — they send power to both the front and the rear by default, so there is no standard two-wheel-drive mode (unlike typical 4x4 trucks with their part-time systems). But there's also a selectable low range for the really tough off-road stuff. In some designs, the driver may have the additional option of controlling how power is apportioned to the front and rear axles through selectable modes and locking differentials.

Part-time 4WD

This type is the real traditionalist of four-wheel propulsion and can most often be found in trucks and SUVs that are designed to work and play in extreme conditions. In this case, the vehicle is typically rear-wheel-drive by default, so the four-wheel-drive system requires the driver to opt in by either pushing a button or shifting a lever. Locking center differentials are par for the course, but many part-time 4WD systems also allow the driver to lock the vehicle's rear differential, which ensures that both rear wheels get power no matter what. Hardcore setups like those found in Mercedes' G-Class or the Ineos Grenadier let you lock the front differential, too — this is the hallowed "triple-locked" configuration that means you'll only get stuck if all four wheels have no traction.

AWD vs. 4WD: Which is best?

Both all-wheel drive and four-wheel drive have advantages and disadvantages, as do each type of four- or all-wheel drive. All-wheel-drive vehicles are typically lighter-duty and are most often used as passenger cars. The added grip in slippery conditions can make for a much safer and more controlled ride in wet or snowy conditions.

In general, all-wheel-drive vehicles like crossover SUVs aren't designed for traversing serious off-road trails or dealing with extreme conditions. Still, their advantage is that they work largely without driver interaction and are usually very reliable. AWD vehicles tend to cost less than comparable 4WD vehicles as well, given the typically simpler and less robust nature of their running gear.

Four-wheel drive can do the same things that all-wheel drive does, like provide grip in slippery conditions on the road or off, but it's also likely that the driver will have to interact with the system more directly. These systems also regularly have more distinct parts, and that can increase possible points of failure.

The simple answer to which is best, AWD or 4WD, is that most people, most of the time, will get along just fine with even the most basic of all-wheel-drive systems. If you regularly go off-road or find yourself in particularly extreme weather conditions, then four-wheel drive might be a better option.