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posted on October 6th, 2017

Winter is coming, arm yourself with knowledge and four wheels

Is your uncle’s 4×4 truck really better than your Subaru, like he says it is? We know that four powered wheels have twice the traction of two, but is a four-wheel drive system better than all-wheel drive? The terms four-wheel drive (4WD) and all-wheel drive (AWD) are often used interchangeably — they do roughly the same thing — but the two systems operate in mechanically distinct ways, are useful in different situations, and are found in different vehicles.

First, a very quick physics refresher. When you turn your vehicle, the outside wheels have to travel farther than the inside wheels, and have to spin faster. A device called a differential sits on the axle between the wheels to allow this difference in speed. There’s also a differential between the front and rear axles to allow your front wheels to turn at a different speed as they turn. Here’s a classic instructional video to explain further.

Say you’re in a precarious predicament, with one wheel off the ground. The differentials will send power to the wheel with the least traction, spinning it in the air. With a functioning 4WD or AWD system, your car will divert power instead to the wheels that do have traction. But to achieve the same goal (traction), each system goes about altering the location of the power differently. These mechanical differences make 4WD and AWD systems advantageous in different situations.

4WD

4WD, also called 4×4, is generally the better system for off-roading.* 4WD locks the front and rear axles together, providing a 50:50 torque distribution. With power delegated equally to each axle, grip and balance are easy to come by. But because the front and rear axles operate at the same speeds, the wheels need to be able to slip some to compensate while turning. On loose surfaces like gravel, sand, or snow, this system is excellent for keeping you from getting stuck, but driving on pavement with 4WD engaged can damage the powertrain of some vehicles. There are mechanical workarounds for this, especially in newer cars, but always be aware of how your 4×4’s system works.

Most 4x4s allow you to engage the 4WD modes manually, giving you more control over how the car moves. When the going gets tough in a part-time 4WD car, you can switch from the default two-wheel drive to 4WD by pulling a lever or pushing a button. If you get stuck in a snowbank, switching to a lower gear 4WD mode should save a call to AAA. 4WD, then, is ideal if you anticipate doing any rock crawling or driving on any particularly dodgy unplowed roads. Many who live in a climate where snow and ice make annual appearances opt for a vehicle with 4WD over AWD. A 4×4 vehicle is also the tool of choice for serious off-roading, dune wheeling, and towing heavy trailers.

Trucks and SUVs typically use a rugged 4WD system to tackle tough jobs and fun off-road outings. The utilitarian Jeep Wrangler still holds its place as one of the go-to all-terrain vehicles, and all modern trucks offer 4WD options. Here are some burly vehicles that do 4WD right:

Mitchell’s Jeep Wrangler (Phoenix, AZ)
Joseph’s Toyota 4Runner (Portland, OR)
Joe’s Jeep Grand Cherokee (San Bruno, CA)
Sam’s Chevrolet Silverado 1500 (Austin, TX)
Frank’s Land Rover LR4 (Alexandria, VA)

AWD

All-wheel drive is the easier system for most drivers. In AWD vehicles, all four wheels are always getting power, though not necessarily in equal amounts. Even the most basic AWD systems sense where the traction is and automatically adjust torque appropriately. In an AWD vehicle, you can go from grippy pavement to slippery snow or dirt without batting an eye. The car does all the thinking for you.

With power going to each wheel in just the right amount, handling abilities are greatly enhanced. This is why AWD is so common with modern sports cars. There are two main downsides to an AWD system. First, cars equipped with AWD are heavier than their 2WD counterparts and thus get worse fuel economy. And because AWD makes use of several integrated electronic and mechanical systems, problems are harder to diagnose and the driver has less control than in a 4×4. But if you don’t plan on upgrading your suspension and conquering the rocky trails of Moab, a car with AWD will be more than fine.

AWD systems vary significantly between manufacturers. Audi’s Quattro system is a famous rally-bred setup that normally has a 60 percent rearward torque bias (60 percent of the power goes to the rear wheels), but can can send up to 100 percent of the power to one axle in a bind. Besides the BRZ, all of Subaru’s models use its symmetrical AWD system, and it seems to be doing the job — just ask a Subaru owner. But just about any AWD system will safely handle rain, snow, and ice with minimal input from the driver. Here are a few reliable AWD vehicles that can give you ease of mind on a slippery road:

Chris’s Subaru Impreza (Laval, QC)
Sarah’s Honda CR-V (Pacifica, CA)
Sandra’s Subaru Forester (Denver, CO)
Jose’s Audi RS 5 (Boston, MA)
Hayel’s Mazda CX-5 (Toronto, ON)

Choose your own adventure

Both 4WD and AWD make winter driving in the mountains much safer, but careful you don’t rely completely on the computers to stay on the road. Winter tires make a world of difference — a 2WD car with winter tires might easily outmatch an AWD vehicle with all-season rubber. Even if you’re piloting a rugged 4×4 truck, it’s a good rule of thumb to always be aware of the condition of your tires’ tread.

For most people, any car equipped with AWD is more than adequate for their three yearly ski trips. A 4×4 has the upper hand for more rugged tasks, but is probably not necessary to own if you’ll only need it a few times. Your decision between the two might come down to the other aspects of the vehicles you’re considering, so don’t get hung up on how a particular AWD system works if a car checks all your boxes.

*Remember, off-roading goes against Turo’s terms of service and will void your protection package.

Steven is an avid car guy and editorial assistant at Turo. Between Golden State Warriors games he can be found getting lost somewhere in California.