Car buyers are ditching sedans, hatchbacks, wagons, and the perennially unpopular minivan in favor of high-riding crossovers and SUVs. Many of the models in this booming segment of the market come with either four- or all-wheel drive, and these two terms are often erroneously used interchangeably. It’s true, the end result is the same: the engine’s power flows to the four wheels. How it gets there is the big difference between the two systems, and choosing one or the other has a big effect on how much fuel your car burns, how much weight it can carry, and how far off the beaten path it will take you.
All-wheel drive is considerably more common in 2019, and it suits the needs of most motorists, but some drivers shouldn’t settle for anything less than four-wheel drive. We’ve broken down the similarities and differences between the two systems to help you decide which one your next car should be equipped with.
Four-wheel drive (4WD)
Let’s start with four-wheel drive. Displayed often as 4WD, and sometimes referred to as four-by-four or 4×4, this system’s main distinction is that it’s typically used on vehicles designed and built to handle the unpaved wilderness. This includes rugged trucks and SUVs such as the Jeep Wrangler, Mercedes-Benz G-Class, and the Toyota Land Cruiser.
In a nutshell, it’s a system that sends power to all four wheels equally and without vectoring (controlling the division of power delivery between the wheels or axles), meaning each wheel will spin at the same constant rate as all the others. Power flows from the engine, through the transmission, and normally into a device known as a transfer case that divides it between the front and rear axles.
The equal split of power is great for maneuvering through tough and low-traction situations, but it isn’t very friendly on the pavement. Driving a four-wheel drive car on solid ground can make simple actions like turning around in a tight street very difficult, because the wheels are no longer in sync.
Most modern 4WD systems are “part-time” and at the flick of a switch four-wheel drive can be engaged
Imagine yourself doing a u-turn. In a four-wheel drive car, the inside wheel has to turn more slowly than the outside wheel, which is covering more ground. You might hear a rubbing noise or feel the car hopping when you approach full lock. This is why most 4WD systems are part-time systems that can be disabled. The car operates in two-wheel drive in normal conditions to improve on-road drivability, but still offers four-wheel traction when you need it.
What about part-time vs. full-time?
Most modern four-wheel drive vehicles are equipped with a part-time system, meaning they operate in two-wheel drive mode in normal driving conditions. The driver can engaged the four-wheel drive system by flicking a switch, pressing a button, or yanking on a center console-mounted lever in low-traction situations.
Some 4x4s feature a transfer case with multiple settings, like 4-Low or 4-High. 4-High limits and vectors available power to the wheels so you can move quickly over slippery surfaces (up to about 60 miles per hour). To get the most available power, however, you’ll want 4-Low, which means 4WD with low-range. This low-range gearbox is for low-speed maneuverability, such as rock crawling or getting unstuck, and is only for such conditions.
You really don’t want to go too fast in 4WD-Low because things will start breaking, and your trip will start getting expensive.
To avoid complexity, a word of advice: You really don’t want to go too fast in 4WD-Low because things will start breaking, and your trip will start getting expensive. Most newer vehicles with part-time systems have an automatic deactivation when the vehicle goes beyond a certain speed to avoid this damage, but older trucks typically do not.
Part-time four-wheel drive systems generally feature locking and unlocking differentials. Between each axle sits a differential that compensates for wheels spinning at different rates. By locking a differential at a front or rear axle, you are inhibiting any slip from occurring at the axle, forcing each wheel at said axle to turn at the same rate.
|4WD pros||4WD cons|
|Best traction in off-road conditions||Adds weight and complexity to cars|
|Can sometimes be turned off to improve fuel economy||Can’t be used in all conditions|
|Proven, rugged technology||More expensive than two-wheel drive models|
Full-time four-wheel drive systems typically don’t come with a two-wheel drive (2WD, or 4×2) mode, so the system is active all the time. It sends power to the four wheels at the same times with limited-slip capabilities. This system is becoming increasingly obsolete, because a part-time system makes more sense for most consumers. Most drivers don’t need four-wheel drive all the time.
Older trucks, such as 1990s Toyota Land Cruisers, have full-time systems. They come with an additional center differential to enable limited slip for better drivability on the road, and the system handles power distribution on its own.
All-wheel drive (AWD)
All-wheel drive is a much more recent innovation, and it’s a little bit more complicated, but also considerably more user-friendly. It crops up on everything from supercars like the Audi R8 to grocery-getters like the Buick Encore. While a four-wheel drive system tries to send as much power to the four wheels as equally as possible for maximum traction, all-wheel drive is all about varying the amount of power sent to each wheel, either mechanically or electronically.
Think of all-wheel drive as similar to the part-time four-wheel drive system, except for cars and some crossovers.
All-wheel drive is often associated with road-going vehicles, such as sedans, wagons, crossovers, and even some larger SUVs. Crossovers like the Honda CR-V, the Toyota RAV4, andthe Mazda CX-3 tend to fall under the “car” category while SUVs like the Chevrolet Tahoe and the Toyota 4Runner fall under the “truck” category. Here’s our article on how to better understand the differences between crossovers and SUVs.
All-wheel drive is similar to the part-time four-wheel drive system we just described, except it’s used on cars and crossovers. It’s also completely automated. The system is constantly active, and it needs no activation or input from the driver to work. Most newer all-wheel drive systems send power to a primarily axle, either the front or the rear, and transfer power away from the slipping wheels when they detect a loss of traction. This helps improve fuel economy. To quote Subaru’s ad campaign, all-wheel drive “transfers power from the wheels that slip to the wheels that grip.”
All-wheel drive is becoming increasingly common in performance applications, too. The Mercedes-AMG E63 is a perfect example. It is now sold only in AWD in the United States because its 600-plus-horsepower output can overwhelm the rear wheels if they try transferring it to the pavement on their own. Even when we aren’t talking about tire-scorching performance cars, splitting power evenly means added stability in all types of weather.
All-wheel drive does have some clear advantages over 4WD.
AWD isn’t quite as robust as 4WD, and it can’t match the acute power delivery necessary for low-speed off-roading like rock crawling. The maintenance and complexity of these systems can also get extraordinarily expensive, but ensuring they function as intended is crucial to your safety.
All-wheel drive does have some clear advantages over 4WD, though. These days, computers are involved in most AWD systems. Sensors on each wheel monitor traction, wheel speed, and several other data points hundreds of times per second. An engine control unit (ECU) analyzes traction conditions and decides which wheel receives power. This type of system, usually called torque vectoring, appears on everything from the Subaru WRX to the Dodge Charger. Torque vectoring has allowed massive improvements in handling and all-weather capability.
Electrified all-wheel drive
Each axle gets its own electric motor so the four wheels are always powered but there’s no mechanical connection between the front and the back of the car. This improves traction and performance while helping clear up passenger space in the cabin because there’s no need for a transmission tunnel.
Some plug-in hybrid vehicles use a blend of technologies to achieve all-wheel drive. Take Volvo’s XC90 T8, for example. The 2.0-liter, four-cylinder engine spins the front wheels while an electric motor mounted over the rear axle spins the rear wheels. It’s front-wheel drive when the four-cylinder works on its own, rear-wheel drive in electric-only mode, and all-wheel drive with both power sources up and running.
|AWD pros||AWD cons|
|Provides increased grip and control under all road conditions||Reduces fuel economy|
|Gives sportier handling and traction to a broader range of cars||Increases the weight and complexity of vehicles|
|Works all the time||Not as good in extreme off-road conditions|
Automakers are getting serious about electrified cars, so these through-the-road all-wheel drive systems will become more common in the coming years.
So, which one do I want?
Ultimately, the system you choose largely depends on your driving needs and where you live. Four-wheel drive is your best bet if you plan on using your vehicle off-road and in difficult terrain on a regular basis. It’s normally found on SUVs and pickup trucks that boast the durability to match the ruggedness of a four-wheel drive system. For most people, however, all-wheel drive makes more sense.
In the sort of winter road conditions most drivers experience, a modern all-wheel drive system that responds instantly and automatically is good enough. Additionally, all-wheel drive vehicles normally have a better weight distribution, which improves traction and performance.
You might not need either, though. If you live in an area where winter is mild at worst, you’d only benefit from having four powered wheels a couple of times a year. We recommend keeping your vehicle simple and cheap, sticking to two-wheel drive, and investing in a good set of winter tires.
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