Although sometimes the terms all-wheel drive (AWD) and 4-wheel drive (4WD) get used interchangeably, they are not the same. In fact, they have very little in common.
To some extent, some automakers muddy the water even further by marketing a variety of AWD and 4WD systems with obscure names. For example, Mercedes-Benz uses 4MATIC, and BMW calls it xDrive.
Why is any of this important? You probably have a good reason to buy a car, truck, or SUV with four drive wheels. Maybe it’s as simple as improving mobility in snow, gravel, and mud. Or, you might have dreams of rock crawling in Moab or taking the family camping in a hard-to-reach spot by the lake.
Do you plan on towing anything?
Focusing on exactly what you want to accomplish with all four wheels under power will pinpoint which system works best for you.
All-Wheel Drive Defined
All-wheel drive is a system engineered for on-road use. AWD sends engine torque to all four wheels simultaneously in its purest form. However, it isn’t a one-size-fits-all system. There are actually two types of AWD.
Full-Time AWD
Full-time AWD sends some amount of engine torque to both axles all the time. The system monitors wheel grip and determines just how much power goes to each set of wheels. When the rear wheels begin to lose grip, the system sends more torque to the front wheels. If the front wheels lose grip, the rear wheels get more power. Under normal conditions, both sets of wheels receive some percentage of torque. Subaru’s Symmetrical AWD you find on the Outback, Forester, and other models is a full-time AWD system.
Part-time AWD
Part-Time AWD sends all the engine torque to either the front wheels (Toyota Camry LE AWD) or the rear wheels (Dodge Charger SXT AWD). That is, under normal driving conditions, vehicles with part-time AWD operate as either front-wheel drive (FWD) or rear-wheel drive (RWD). When the system senses some slippage in the primary drive wheels, it transfers some amount of engine power to the other axle.
The key for both systems is that all of this transferring of engine torque from axle to axle works transparently. The driver doesn’t take any action. It’s all automatic. True, some AWD vehicles allow the driver to engage a driving mode for more extreme conditions. For instance, Subaru’s X-Mode standard on the Outback and offered on the Forester is such a feature. X-Mode tweaks the powertrain response and other functions to ultimately enhance traction. Generally, however, the driver doesn’t need to take any action for AWD to function.
4-Wheel Drive Defined
Whether you call it four-wheel drive, 4-wheel drive, 4WD, or 4×4, it is typically a part-time system engineered more for off-road driving than dealing with roads affected by foul weather. In most cases, the driver must shift in and out of 4WD.
Some 4WD systems are more complex and capable than others. But when the driver shifts into 4WD, it locks the front and rear axles together, meaning all four wheels receive equal power and rotate at the same speed. Once engaged, 4WD systems don’t rely on a computer to sense wheel slip.
All wheels have power. If one or two wheels lose grip, the other wheels propel the vehicle forward. You will find 4WD systems in vehicles like the Jeep Wrangler, Ford F-150 Raptor, Ram 1500 TRX, and Chevrolet Colorado Bison.
How All-Wheel Drive Works
What many AWD systems have in common is a center differential located between the front and rear axles. A computer and sensors monitor the primary drive wheels for wheel slippage. When slippage occurs, the system transfers engine power to the other axle via the center differential.
Other AWD systems may employ more than one differential, multi-plate clutches, or viscous couplings to help swap power from axle to axle.
Typically, the power split is up to 50%. Some systems, however, can shift as much as 100% of power back and forth between axles. The Acura Super-Handling AWD (SH-AWD) system does this. But, the more sophisticated AWD systems, such as Acura’s SH-AWD, also have torque vectoring. This is a big help in cornering on dry pavement because a torque vectoring differential on each axle slows the rotation of the inner wheel while accelerating the rotation of the outer wheel in a turn.
In terms of slick surfaces, torque vectoring can shuffle as much as 100% of an axle’s power back and forth to one solitary wheel, if necessary. The brake lock differential on the Jeep Grand Cherokee QuadraTrac full-time AWD system employs anti-lock brakes to mimic torque vectoring.
AWD Pros
Added traction in bad weather
Operates automatically and seamlessly
System reaction is quicker than a human’s
More fuel-efficient than 4WD
Added value if you sell
AWD Cons
Cost
Not engineered for more extreme situations
How 4-Wheel Drive Works
Not always, but most commonly, 4WD is a part-time system. As we’ve already pointed out, various automakers take different paths to power all four wheels. But to keep things simple, most 4WD systems work part-time.
Unlike AWD systems, relying on a computer to shift engine output to all four wheels, 4WD systems require some driver participation to get the most performance out of all the wheels. This means the driver must engage the system at some point by way of a button, dial, or shift lever. A true 4WD system should never be engaged on dry pavement.
It’s not wise to use 4WD on anything but slippery, loose, or rugged surfaces because both axles lock together, with all four wheels rotating at exactly the same speed. This isn’t much of an issue when traveling in a straight line on dry pavement. However, in turning the vehicle, the outside wheels must turn faster than the inside wheels.
This creates a situation where, in 4WD, the wheels on one side of the vehicle fight the wheels on the other side. This puts a lot of stress on the system. It’s a sure way to cause damage. On slippery or loose (gravel) surfaces, though, all four wheels are free to slide and travel their own arcs through a curve without stress.
Gear Settings for a 4WD Vehicle
2-wheel drive (2WD) or 2-Hi is the normal mode for dry pavement. In 2-Hi, a vehicle functions as a RWD vehicle.
4-Hi brings all four wheels to bear, locking the axles together with a fairly even split of engine power to each.
4-Low or 4-Lo usually requires you to bring the vehicle to a full stop to make the transition from 4-Hi. This is the gear for extreme conditions. 4-Low gearing generates more torque for difficult, low-speed situations.
There are some higher-end 4WD systems with an automatic setting for 4-Hi. The system is engineered to allow the outside and inside wheels to rotate at different speeds when in 4-Hi. These 4WD systems then function like an AWD system most of the time.
When conditions become too extreme for 4-Hi, the driver must take charge and manually shift into 4-Low.
4WD Pros
Off-roading capability
More towing capability than AWD
Extra weight of 4WD contributes to improved traction
4WD Cons
Poor fuel economy
Can’t safely operate on dry pavement
Additional weight increases stopping distances
AWD vs. 4WD With Ice, Snow, and Rain
In a nutshell, if all you are looking for is a bit of extra peace of mind when driving in foul weather conditions such as ice, snow, sleet, and rain, AWD is the way to go. AWD removes some of the drama from snow and ice driving.
If you deal with extreme snow and ice, 4WD is the ticket.
If you also want to off-road into the wild, 4WD works better if you want to wander off the pavement. Also, 4WD vehicles tend to offer far more towing capacity than AWD vehicles. But all that extra 4WD capability comes at a price. While the extra weight of 4WD helps traction, it is a big disadvantage at the gas pump.
AWD brings the advantage of being a seamless system. Power goes to all four wheels when the AWD system senses it’s needed and back to two wheels when it isn’t. Many AWD systems add very little weight to the vehicle and, therefore, have little impact on fuel economy.
What Is 2-Wheel Drive?
Most vehicles generate their propulsion using either the front or rear wheels. Even most AWD and 4WD vehicles act like 2-wheel drive vehicles when conditions allow. Cars with only two drive wheels have the advantage of being lighter and burning less fuel than those with AWD or 4WD.
Front-wheel drive cars tend to be lighter than RWD cars because they don’t require all the hardware required to distribute power to the rear wheels. Front-engine FWD vehicles are better suited for foul weather because most of their weight is over the drive wheels. RWD vehicles offer better cornering performance than FWD.
Car vs. SUV vs. Truck: Which Is Better for AWD or 4WD?
Here’s the thing: Most pickup trucks only use 4WD. (Exceptions to this are the Honda Ridgeline, Ford Maverick, and the Hyundai Santa Cruz. All offer AWD). AWD is exclusive to cars and minivans. Only SUVs/crossovers accommodate both. So, it’s not so much about which platform works best for AWD and 4WD, but which type of vehicle do you want or need.
If your answer to that is a pickup truck, you have little choice other than 4WD. Likewise, if a minivan or car is your vehicle of choice, it’s AWD.
RELATED: Driving in Snow: Top Tips You Need
Truck-based SUVs typically use a 4WD to power all four wheels. Car-based crossovers use AWD. Truck-based SUVs usually offer more ground clearance, which is good for getting over obstacles and snow. They also boast more towing capability.
Although some crossovers like the Subaru Outback tout impressive ground clearance (8.7 inches), for the most part, crossovers have less ground clearance than a truck-based SUV. They are also poorly suited for straying very far off the pavement.
The best answer to the right combination of vehicle type and 4WD configuration is the one suiting your needs.