The middle of summer may not seem like the right time to worry about the differences between all-wheel drive and four-wheel drive, but it’s certainly not something you want to save for the middle of a howling blizzard, either. In fact, because both of those technologies provide benefits in a wide variety of driving situations, understanding the differences between the two is an important part of shopping for a new or used vehicle.
This is easier said than done though, since not even the automakers can fully agree on what those differences are.
Both all- and four-wheel drive do rely on the same concept. Instead of having the engine send power to just the front or rear wheels, as in a traditional car, AWD and 4WD systems route energy to all four wheels. That way, if one or more wheels loses traction, the other(s) can still rely on engine power to help move the vehicle.
The classic definition of four-wheel drive, from new-car buying site Edmunds.com, for example, generally has to do with the presence of a transfer case. In these systems, it’s the transfer case, as its name indicates, that transfers power from the engine to all four wheels. Most often, the old-school systems rely on a chain or set of gears to get the job done, but there are two more important factors on these older systems. One is that drivers have to switch from two- to four-wheel operation manually, and the other is that transfer cases have different gear ratios for two distinct driving situations: one for everyday driving and then a separate, lower gearing specifically for off-road performance.
Today, some automakers do continue to offer these traditional, transfer case-based four-wheel drive systems. But companies also have been able to leverage the latest computer technologies to provide new ways to drive all four wheels in a vehicle. In the most sophisticated of these systems, sensors determine exactly which wheel(s) have the best traction, then automatically adjust power delivery on an individual basis. There’s no need for driver intervention, or a transfer case. These systems, typically designed for better on-road performance in bad weather, are what the majority of auto brands call “all-wheel drive.”
Let’s take a look at the Chrysler 200 and Jeep Cherokee, both manufactured by Fiat Chrysler Automobiles and both offering powertrains that drive all four wheels. The Jeep engineering team says that each vehicle offers powertrain technologies that “are very similar in a number of ways,” with the big differences being the “functional requirements” for each vehicle.
In the 200 midsize sedan, all-wheel drive "provides inclement-weather traction and spirited dynamic performance in all conditions, without any needed driver input,” the Jeep engineering team says. Meanwhile, the Cherokee SUV builds on the same basic technology, then adds an advanced terrain management system with four driver-selectable settings. Here, each setting changes how torque is sent to the four wheels, but without the exclusive off-road-friendly low gearing that comes with a transfer case.
According to Jeep, it’s the terrain management feature, with some help from a locking differential, that gives the Cherokee its “four-wheel drive” capability; and to be clear, that’s because the technology provides distinctly different drivetrain modes, for travel on “snow,” “mud,” “sand” and “rock,” and they let the driver control exactly which setting is being used.
This is where things get tricky, however. You see, the Cherokee does offer a transfer case for its most capable Trailhawk model, and that, with separate gear ratios for “low” four-wheel drive, serves up the kind of hardcore 4WD ability most people think of when they think of Jeep. But remember, the brand uses the term “four-wheel drive” even for those Cherokees without a transfer case, because they still check off the boxes mentioned above. Other brands, including Ford, Nissan and Land Rover, do the same thing: use “4WD” to cover a system that provides power to all wheels, using driver-controllable settings for improved traction in different driving scenarios, all without necessarily needing a transfer case.
Meanwhile, Subaru’s “Symmetrical All-Wheel Drive” is a permanent setup that delivers power to all four wheels even in clear driving conditions.
There’s also a whole new wave of all- and four-wheel drive technology that has recently started entering the marketplace. Cars like the Acura RLX Hybrid, along with crossovers including the Volvo XC90, have begun combining gas engines for the front wheels with electric motors to drive the rears.
Jim Nichols, technology and product communications manager for Volvo Cars North America, says, “Overall, the Volvo AWD system provides more responsive traction and handling when compared to other four-wheel drive and traditional AWD technologies. It is more fuel-efficient and provides power precisely where it is needed in a variety of conditions -- whether they be low traction, steering or heavy acceleration. This allows for a more adaptive driving experience in a variety of conditions.”
What does that all mean for drivers? To get the vehicle that best matches your driving requirements, don’t get hung up on what a drivetrain system is called, but do focus on what the technology does.
Generally speaking, mainstream cars and crossovers will offer “all-wheel drive” that provides most of the engine power to the front wheels most of the time. But if those wheels start losing traction, the system can automatically send some of the torque to the back, where it can still be used. Even the Jeep team indicates this sort of AWD is enough for “sure-footed traction” for drivers who stay on the pavement and don’t regularly face extreme weather conditions.
SUVs and SUV-style crossovers, along with pickup trucks, will often provide systems that offer more driver control for a wider variety of conditions and road surfaces, and sometimes also include technology specifically for true off-road driving.
While it may seem confusing at first glance, most brands do make it easy on shoppers in at least one sense: It’s rare that a mainstream brand offers multiple all-/four-wheel drive systems for the same vehicle. In nearly all cases, there’s a standard drive configuration and then one other that is specifically aimed at boosting the vehicle’s core capabilities. Family-friendly mainstream vehicles, like the all-wheel drive Chrysler 200 mentioned above, tend to provide front-wheel power in typical driving scenarios, then can automatically route torque to the rear wheels when slippage up front is detected.
The result is a noticeable advantage in traction when the roads get slippery, but drivers headed off road -- or who could encounter extreme weather conditions -- may prefer the added confidence of a four-wheel drive vehicle. In those choices, whether they have a transfer case or terrain management technology, owners can pick driving modes that are specifically designed for unique road conditions, and that includes conditions where there are no roads at all.