What you need to know about all-wheel drive and four-wheel drive

In the olden - and generally less confusing days -  days, if you wanted a vehicle with four driven wheels, you were limited to a handful of bakkies or serious offroaders (Think the original Landrover Defenders, Nissan Patrols and Toyota Landcruiser “Troop Carrier” Wagons).These vehicles were either hardworking workhorses or serious off-road Namib-capable go-anywhere off roaders.

But times have changed. Now every second or third moms’ taxi, hatchback or small SUV are equipped with either all-wheel drive (AWD) or four-wheel drive (4WD).

Just think of the various Volvos, Audis and Subarus on our roads. You’ve probably noticed that little “AWD” sticker or decal somewhere on the bootlid, or “Quattro” in the case of Audis. There’s also “4Motion” on VWs. What exactly does that mean though? And why do you need it?

As the name suggests, all wheel drive means that the vehicle can send power to both the front and rear wheels. But what's the difference between AWD and 4WD?

And which is right for you? Are you planning on joining a 4X4 club and going dune driving in Namibia? Or is just keeping up with the Jones’ and every other mom in the parking lot at Crawford Lonehill?

AWD vs. 4WD terminology can sometimes be confusing, with the lines and preconceptions getting even more blurred as AWD systems have become more robust and 4WD has gotten more sophisticated. And of course, to confuse things further, various manufacturers often use these terms differently.

Here's how each system works and the advantages and disadvantages of each. With this knowledge, you can make an informed decision when shopping for your next SUV, Bakkie or car.

What is all-wheel drive?

The answer is in the name - All-wheel-drive systems means the car can potentially send power to all four wheels, which is not to say that it always does so. In practice, there are actually two types of drivetrains that are called AWD. One does, in fact, drive all the wheels continuously, and some manufacturers refer to this as full-time AWD. The second, often called part-time AWD or automatic AWD, operates most of the time in either front-wheel drive or rear-wheel drive, depending on the vehicle's drive system. In these systems, power is delivered to all four corners only when additional traction control is needed.

How does all-wheel drive work?

Both full-time and part-time systems generally operate autonomously and require no input from the driver, although certain manufacturers  offer selectable modes that allow a degree of control over how much power goes where.

Sending torque to all four wheels is achieved through through a series of differentials, viscous couplings and/or multi-plate clutches, which help distribute power to the wheels so that the car's traction is optimized. The vehicle still operates smoothly under normal conditions.

Full-time AWD

In full-time AWD, both the front and rear axles are driven all the time. The advantages of AWD over regular two wheel drive cars is better grip, better traction and generally quicker acceleration from stationary. On dry roads, this kind of AWD can help the vehicle handle better and ensure that full power gets to the road. And in slippery conditions, such as ice, snow or mud, it provides always-ready traction for safer, more confident handling. The early Audi Quattro systems were good examples of full time AWD.

Part-time AWD

In normal operation, part-time AWD sends torque to two driven wheels, either the front or rear, depending on the make and model. The part-time system then automatically engages the other wheels when road conditions demand extra traction. Modern part-time AWD uses an array of electronic sensors that feed information to a computer, which controls the amount of power directed to each wheel. This setup is commonly found on car-based crossovers and AWD cars.

Certain people believe that full time 4WD is not fuel efficient like part time 4WD. It just takes more power to make all those gears, front and rear, work. And more moving parts means more wear and tear, and abuse, on the whole drive train, unlike part time and only two wheels are being driven. In situations where you do not require power to be sent to all 4-wheels, such as long distance driving on good quality tar roads, one may save a little in fuel and wear and tear on your vehicle by only driving two wheels.

All-wheel-drive pros and cons

The best thing about full-time AWD is that the driver doesn't have to make any decisions about engaging the system. A good part-time AWD will also work autonomously, where the system itself is designed to sense loss of traction and send power where it's needed. However, older systems tended to lag before they kicked in, so you had a fun few moments of wheel-spinning and mud-hurtling before traction and power was responsibly redistributed to the wheels which needed it most.

Nowadays, AWD is available on a wide variety of vehicles in South Africa, from compact sedans to performance models to all sizes of SUVs, giving you a broad range of choices.

AWD is able to work well in a variety of conditions, from rain to snow to light off-roading, but it's considered a lesser choice by serious off-roaders. (People have been shot for lesser offences than pitching up at certain 4x4 clubs on the East Rand in an AWD vehicle. Adding insult to injury is when these stock-standard AWD vehicles go on to outperform and embarrass top end 4x4’s with low range transfer boxes and lockable diffs, old man emu suspension and a snorkel the height of Ponte).

This perception is changing somewhat as modern AWD systems get better and more capable, but many drivers who like to venture far off the beaten path prefer the capability of a two-speed transfer case with low-range gearing, more on which below.

In terms of disadvantages, compared to regular two-wheel drive vehicles, AWD also increases the cost of a vehicle, adds weight to the vehicle,  and, in most cases, will reduce fuel economy.

What is four-wheel drive?

This is the more traditional system that comes to mind when most people think of drivetrains that power all four of a vehicle's wheels. The stereotypical picture of a 4WD vehicle is of a truck with high ground clearance, a massive bull bar, a shielded underbody, tow hooks and big, knobby tires. And it is true that this system is found primarily in trucks and SUVs.

However over the years, 4WD engineering has become increasingly sophisticated, and although it generally remains capable of more serious off-road use, it can now be found on a wider variety of comfortable, even luxurious, models. 4WD systems deliver torque through a series of front, rear and centre differentials, transfer cases and couplings, which allow the vehicle to operate at maximum traction under a variety of conditions.

How does four-wheel drive work?

Like AWD systems, 4WD is designed to maximize traction front and rear. But 4WD systems tend to be more robust than AWD ones and can generally handle more rugged terrain. And they, too, come in two types: full-time and part-time.

Traditional 4WD systems have a two-speed transfer case with high- and low-range modes that can be selected by the driver, either with an electronic switch or a mechanical lever. The low-range setting multiplies torque to provide maximum traction in low-speed off-road environments. The high-range setting is useful for less challenging off-road scenarios as well as slippery on-road conditions, such as packed snow, ice, loose sand or gravel.

Full-time four-wheel drive

Full-time 4WD operates as a full-time AWD system does, with all four wheels receiving power on a continuous basis. Late-model Toyota Land Cruisers are a good example — they send power to both the front and the rear by default, so there is no standard two-wheel-drive mode (unlike typical 4x4 trucks with their part-time systems), but there's also a selectable low range for the really tough off-road stuff. In some designs, the driver may have the additional option of controlling how power is apportioned to the front and rear axles through selectable modes and locking differentials.

Part-time four-wheel drive

This type is the real traditionalist of four-wheel propulsion and can most often be found in trucks and SUVs that are designed to work and play in extreme conditions. In this case, the vehicle is typically rear-wheel drive by default, so the four-wheel-drive system requires the driver to opt in by either pushing a button or shifting a lever. Locking center differentials are par for the course, but many part-time 4WD systems also allow the driver to lock the vehicle's rear differential, which ensures that both rear wheels get power no matter what. Hardcore setups let you lock the front differential, too — this is the hallowed "triple-locked" configuration that means you'll only get stuck if all four wheels have no traction.

Four-wheel-drive pros and cons

There's no substitute for true 4WD in tough off-road scenarios. Even though 4WD systems are now available in well-appointed luxury bakkies and SUVs, at heart they are designed for ruggedness and maximum traction when you need it most, so they are the right choice for difficult terrain.

These days, 4WD design has become increasingly refined. But, depending on the make and model, 4WD vehicles still often deliver a stiffer ride than their two-wheel-drive counterparts. These systems also have a detrimental effect on fuel economy and increase the initial and maintenance costs of the vehicle.

Do you need AWD or 4WD?

Unsurprisingly, the answer to the AWD vs. 4WD debate is that it depends on where you live and what kinds of driving conditions you encounter, as well as personal taste.

AWD can be found in cars, bakkies and SUVs of all sizes, from compact to full-size, giving you the widest possible range of vehicles to choose from. It delivers increased traction in normal winter conditions or light off-roading and provides the fewest compromises in ride and fuel economy on dry roads. And it has the advantage of either powering all four wheels on a continuous basis or automatically controlling which corner gets the torque, taking the decision-making process out of the driver's hands.

But 4WD is still the better choice for those who need to work in extreme weather conditions or enjoy off-road adventuring. This system often comes in bakkies and SUVs with higher ground clearance than average, making them well suited to managing deep snow, the potholes on Rivonia road, rocky terrain and steep grades, as well as carrying or towing heavy loads. In addition, the two-speed transfer case with low- and high-range gearing gives the driver the greatest amount of control over where and how the power is delivered, especially when paired with multiple locking differentials.

This article has been based on and adapted from Edmunds.com (https://www.edmunds.com/car-buying/awd-vs-4wd-whats-the-difference-and-which-to-choose.html)