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RWD, AWD, 4WD or FWD: What Does it All Mean?

Photo by Jaguar MENA on Flickr / CC BY 2.0.

As a driver, you need to consider some important questions about safety. Is your vehicle’s wheel drive system appropriate for your driving habits and the roads you typically travel? Do you even know what kind of system you use? Most drivers have a hard time understanding the advantages of different options, and it’s hard to blame them; the technical details could confuse almost anyone. Fortunately, this guide should clarify the issue.

Automakers offer plenty of drive options, but you’ve generally got four different configurations to choose from. These include rear-wheel drive (RWD), front-wheel drive (FWD), four-wheel drive (4WD) and all-wheel drive (AWD). Here’s a quick guide to each:

Rear-Wheel Drive: Pushing from the Back End

BMW 550i M-Sport. Photo by Aurimas on Flickr / CC BY-ND 2.0.
BMW 550i M-Sport. Photo by Aurimas on Flickr / CC BY-ND 2.0.

If you’ve ever ridden a bicycle or a motorcycle, you’re already familiar with rear-wheel drive. This technology, developed in the 1800s, applies force to the back wheel or axle to propel the whole vehicle forward, passengers, cargo and all.

As the first automobiles were developed by pioneers from across the globe, most incorporated similar layouts with front-mounted engines driving the back wheels. The RWD configurations of the modern era, however, are most often found on trucks and other heavy-bodied vehicles. In comparison to many other options, having the drive wheels in the back provides powerful acceleration; the rear wheels can dig in and give you a nice push forward.

The downside of connecting a forward-mounted engine to the rear axle is that doing so requires a number of heavy, bulky parts that weigh the chassis down and decrease fuel efficiency in the process.

Although RWD vehicles generally get lower fuel economy, they also have some advantages. For instance, decades of tinkering and refining have resulted in modern racers that dominate competitive circuits and tracks with smoother handling and balance. Some of the techniques routinely employed by top drivers, like swinging vehicles through tight corners, are possible largely because of RWD configurations.

Front-Wheel Drive: Consolidating Vehicle Design

Photo by Bull-Doser on Wikimedia Commons / CC0 1.0.
Photo by Bull-Doser on Wikimedia Commons / CC0 1.0.

In the late 1970s, motorists and automakers started growing increasingly conscious of concepts many of us now take for granted. Chief among these was fuel economy: The 1970s oil embargo and various environmental concerns shifted the public demand towards cars that cost less to run, manufacture and maintain. The front-wheel drive configuration, which groups the engine, differential, transmission, drive axle and other components right on top of each other, has proven to be a highly efficient design for reducing overall material and operating costs.

Variants of the FWD layout have since become some of the most common systems in passenger vehicles, and are most often found in compact and mid-range cars. FWD owners already enjoy better gas mileage, but they might be able to raise their efficiency further by carrying more passengers or luggage per trip. These compact drive train arrangements leave plenty of extra space for people and cargo.

What about the handling aspects? The FWD vehicle’s stacked drivetrain model is perfect for navigating through snow, mud and other slippery or layered terrain. Because the drive axle mounting supports the weight of the engine and other parts, the wheels get pushed downwards more. In hazardous conditions, FWD vehicles will exhibit better grip.

On the other hand, FWD drivetrains might also result in uneven transfer of weight throughout the vehicle. The front brakes and tires have to do the majority of the work when you decide to speed up or slow down. As a result, forward components may require more frequent maintenance or replacement.

Four-Wheel Drive: The Best of Both Worlds?

Instead of relying on the differentials used between the front and rear axles of other vehicles, 4WD vehicles usually employ a device known as a transfer case. Transfer cases take power from the transmission and put it to good use by rotating the rear and front axles.

Innovative chain-drive mechanisms and gearing arrangements allow transfer cases to perform unique situational functions; for instance, they’re often used to keep out-of-sync axles spinning at the correct speeds in on-road vehicles fitted with bigger back tires. Off-road enthusiasts also use transfer-case-equipped vehicles to selectively lock their axles so that they can power through mud and frozen ground.

Most 4WD vehicles function in front or rear two-wheel drive mode until you decide to engage all four wheels. These trucks, SUVs and other large-chassis vehicles’ axles can be operated in a locked-together mode, so 4WD is great for maximizing usable torque when you can’t count on much traction.

All-Wheel Drive: Tackling All Terrain

In reality, AWD is actually a type of four-wheel drive. What sets it apart is the fact that it incorporates a differential. According to the AWD Wiki:

A differential is the driving-axle gear assembly located in the center housing between the driving wheels on rear-wheel drive vehicles, or as part of the transaxle on front-wheel drive vehicles or between front and rear differentials on all-wheel drive vehicles. The differential transmits power to the wheels while allowing each wheel to rotate at different speeds, such as when turning a corner.

This special gearing assembly is used to let a vehicle’s wheels spin at ideal speeds when you’re traveling through turns or over slippery terrain, like ice. Under conditions such as these, your right and left wheels may have to travel different distances, so the vehicle basically allows them to rotate independently.

Although they were invented much earlier, AWD vehicles started gaining their popularity during the 80s. While these high-traction configurations were once limited to fancy sports cars, their practicality and ease of use helped them spread throughout the entire vehicle market. In fact, according to Polk, more than one third of vehicles sold in the U.S in 2010 were equipped with either AWD or 4WD.

Those who prefer AWD vehicles often cite the fact that they can take advantage of their features without doing anything special. Because these systems are generally smart enough to send power to whichever wheels require it most, they have great situational traction and handling characteristics. You don’t have to decide which axle or wheels to power, even when you’re traveling off road, and the lockup problems that plague some 4WD off-roaders are conspicuously absent with AWD arrangements.

It’s true that AWD vehicles usually cost more when they’re new, but depending on market, they tend to retain higher market prices as they age. Even though you might have to settle for paying more initially, the superior traction could assist in an accident!

So which drivetrain is best for you? In the end, it all comes down to your driving habits and long-term goals. Consider what it takes to stay in control on the roads you routinely tackle, but also think about where your journeys might take you down the line. Check back soon for more great tips on choosing the best vehicle features for your needs.