Shop for a vehicle, especially an SUV, and you may find all-wheel drive (AWD) and four-wheel drive (4WD) listed as available choices. In both cases, power goes to all four wheels when these systems are operating. While these two systems work well in slippery conditions, handling isn’t always improved, and there is no added benefit in braking. We’ll examine both systems to outline their similarities and differences.
AWD vs. 4WD: A Matter of Differentials
So, what’s the difference between AWD and 4WD? They sound the same, so they must operate in like manner, right? Well, no. There are distinct differences, even the seller cannot offer a convincing explanation.
Vehicles equipped with AWD come with center, front and rear differentials; a differential is essentially a box of gears used to tap power from the transmission. In effect, an AWD system sends power to the wheels with the most grip by utilizing the center differential. Power may be split between two wheels on either the front or the rear axle, and it may also send power to all four wheels at varying levels.
Deciphering All-wheel Drive
Most AWD systems are based on front-wheel-drive platforms, and they’re often used with the car-based architecture utilized by many of today’s crossovers. Mainstream cars employing AWD include the Subaru Legacy and the Nissan Altima SR. Luxury models with AWD include the Audi A6. The Subaru Outback, Ford Edge, and Audi Q5 are examples of crossovers offering AWD.
In almost all cases, power is distributed to axles or individual wheels as needed. AWD systems are always on, ready to distribute power in a way that optimizes grip in the current driving situation.
Examining Four-wheel Drive
While AWD usually corresponds to cars, 4WD is typically used with truck platforms, and you’ll find it in pickups like the Toyota Tacoma and Ford F-150. However, few of today’s SUVs use them, with the Toyota 4Runner and large models such as the Ford Expedition, Nissan Armada, and GMC Yukon among the notable exceptions.
Most SUV manufacturers have transitioned away from truck-based (body-on-frame) designs to car layouts for improved body rigidity, superior handling, and better fuel economy.
The High and Low of 4WD
Vehicles equipped with 4WD utilize two differentials and a transfer case. In this arrangement, each axle has a differential, with the transfer case tasked with splitting power between the two.
Contemporary 4WD systems are usually activated by means of a dial or switch found in the cabin and often have High and Low 4WD gears. When placed in High you can travel at higher speeds, up to a certain limit as outlined in your owner’s manual.
When operating in Low, low-range gearing is at work, supplying you with more power when climbing rocks or navigating through the sand. Further, if you’re stuck in a rut, low-range gearing is what will free you. You won’t use Low range elsewhere as it is designed solely for low-speed driving.
An Electrified Variation on the AWD Theme
Some electric cars and hybrids, such as the Tesla Model S and the Acura RDX SH-AWD, also employ AWD, but not in the traditional sense.
For the Model S, there is no mechanical connection (center differential) connecting the two axles. Instead, there is one electric motor powering the front wheels and one or two electric motors on the rear axle, with a computer controlling how power is distributed between the axles and wheels.
Acura uses a similar arrangement with the AWD system found in select RDX models, but the manufacturer also utilizes a gasoline engine for improved performance. Here, you’ll find an electric motor working with a traditional transmission up front and a pair of rear electric motors operating independently at each rear wheel.
AWD Systems That Mimic 4WD
Manufacturers sometimes market AWD models as 4WD. These systems can do a fairly good job of mimicking 4WD, but they do so without a transfer case.
For instance, certain 2017 Ford Explorer models come equipped with what the automaker calls “intelligent 4WD” and a terrain management system. The first term uses a computer to automatically manage handling and traction, balancing the way the power is split between the two axles. Meanwhile, the terrain management system allows the driver to dial in settings for specific conditions such as sand, mud, snow and gravel. In truth, this is a sophisticated AWD system providing benefits similar to 4WD.
Now that you know the differences between AWD and 4WD, you can shop accordingly. That said, keep in mind that both AWD and 4WD add weight to the vehicle, which often reduces fuel economy. Lastly, neither system is a substitute for safe driving.
See Also — All-Wheel Drive Comes to the Toyota Camry
Photos copyright Stumpwater Media Group, LLC.
