What’s the difference between 4WD and AWD?
SUVs and crossovers have grown in popularity over the last decade or so, particularly with families and people who enjoy an outdoorsy lifestyle.
Double-cab utility vehicles, or utes, have joined this trend in more recent times. The extra ground clearance of these vehicles elevates the driver, providing improved visibility of the road ahead, especially in heavy traffic. What’s more, SUVs, crossovers and double-cab utes typically come with more cargo space than a sedan or hatch. This load space appeals to many drivers with young families or outdoor sporting equipment to transport.
Most of these vehicles include models that are either four-wheel drive (4WD, 4x4, four-by-four) or all-wheel drive (AWD). Both systems transfer power from the engine to all four wheels, but they do so in very different ways. This can result in quite different vehicle weights, towing capacities, driving characteristics, maintenance costs and fuel economy. So even though many people use either term to describe both systems, it helps to understand the differences when choosing a vehicle for you and your family.
At a high level, all-wheel drive is much more common these days because it suits most people’s needs. But four-wheel drive is still preferred by many, such as those who tow a large trailer boat or regularly drive in challenging off-road conditions. To help you make a more informed choice, here’s a summary of the main differences between each system.
Four-wheel-drive (4WD) explained
The four-wheel drive system is typically used on vehicles designed for the rigours of off-road driving. They’re built tough to handle challenging terrain like boulders, river crossings and seriously uneven landscapes.
In its basic form, a four-wheel drive system drives all four wheels equally, so they all turn at exactly the same rate. Power from the engine passes through the transmission and into a transfer case, which separates it to the front and rear axles.
When it comes to driving in tough terrain and on slippery surfaces, the even division of power and equal rotation of every wheel is great. But on normal smooth road surfaces things like doing a tight U-turn can be difficult.
When you turn a car, the outside wheels have to cover more ground than the inside ones, so they need to be able to turn at different rates. Try a tight turn in 4WD and the vehicle will either feel like it’s doing small jumps or you’ll hear a rubbing sound. To avoid this, the majority of four-wheel drive systems let you disable them when you need to. These are known as part-time 4WD systems. With the 4WD system disabled you essentially have a normal two-wheel drive system for normal conditions and improved on-road driving. All the 4WD capability can still be selected when you need it.
Part-time 4WD vs full-time 4WD
The vast majority of today’s four-wheel drive vehicles have a part-time system, so for everyday driving you simply select two-wheel drive. If you want to use four-wheel drive for rough terrain, towing or slippery surfaces, you simply select four-wheel drive using a button, switch or lever.
Some part-time systems let you select a low or high four-wheel drive mode. The low mode is designed to deliver maximum power in very low-speed situations, such as when you’re bogged in or want to crawl over rocks. If you try to drive at any sort of speed while in 4WD-Low you’re likely to damage or break your drive system. Fortunately, to avoid this kind of expensive disaster, most of the more recent part-time 4WD systems automatically switch out of low mode above a pre-set speed. High mode is ideal for driving in slippery conditions where you also want to maintain a reasonable speed.
Another common feature of more recent four-wheel drive systems is the ability to lock and unlock the differentials. Locking the front or rear differential forces both wheels on that axle to turn at the same speed, which can be ideal for some types of difficult terrain. Unlocking the differential again allows the wheels to turn at different speeds, making tight cornering easier.
Some part-time 4WD systems even let you select the ideal combination of settings for a range of driving conditions at the push of a button.
As their name suggests, full-time 4WD systems don’t give you the option to switch to two-wheel drive, also known as 2WD, 4x2 or four-by-two drive. So you’re always in 4WD mode, where the power is sent to all four wheels - typically through limited-slip differentials that provide a limited ability for wheels on the same axle to turn at different speeds. Full-time 4WD systems are mainly found in vehicles from the 1990s or earlier. Consumer choice is making them more and more obsolete, because most people want the option to use the more economical 2WD for everyday driving.
All-wheel drive is like the modern alternative to part-time 4WD for people who will never need low-speed 4WD grunt to crawl over rocks or escape after becoming stuck in mud. The main difference between the two systems, and it’s a big one, is that instead of trying to send equal power to all four wheels, all-wheel drive tries to send exactly the right amount of power to each wheel individually. Whether it does this electronically or mechanically, it does mean a more complex and expensive-to-repair system. It is, however, much easier to use.
All-wheel drive systems are fully automated, so the driver doesn’t need to do anything in terms of power distribution between the four wheels. You don’t need to turn it on or off or choose different modes. It’s always on, always sensing what is required and always delivering the best power distribution for optimal road handling and safety.
To optimise fuel economy, most of today’s AWD systems deliver power to a main axle by default, either the rear or front one. This essentially creates an initial 2WD system. But if one wheel starts to lose traction, the AWD system immediately starts to transfer power to other wheels.
Most AWL drive systems are computer controlled. Each wheel has sensors that collect information hundreds of times each second on things like rotation speed and traction. A central control unit constantly analyses the data. It can adjust how much power each wheel gets in a split second. Known as torque vectoring, this system has led to significant handling improvements in all kinds of challenging weather.
All-wheel drive systems are not as robust as the grunty 4WD systems. They’re also very complex, which can increase maintenance costs and make components expensive to replace if required. But if they’re checked according to the manufacturers schedule and kept in good shape, they’re remarkably good at helping to keep you and your passengers safe.
Understandably, all-wheel drive has found a home in vehicles that mainly live on the road, never venturing into rough and challenging terrain. Today’s sedans, hatches, crossovers and larger SUVs often come with an AWD option. And because the latest AWD systems can distribute large amounts of power exactly as required to each wheel, in the blink of an eye, you’ll also find AWD in high-end supercars.
All-wheel drive and electric vehicles
Some cars these days can be built with two electric motors, one on each axle, coupled to advanced all-wheel drive traction systems. So there’s intelligent power delivery to all four wheels.
Plug-in hybrid vehicles have both an electric motor and an internal combustion engine. In some of these a good sized four cylinder engine drives one axle and an electric motor drives the other. This means it’s 2WD in electric only mode or when only using the internal combustion engine, but all-wheel drive can be selected, which allows both engines to run at same time.
Choosing between 4WD, AWD and 2WD
The main thing to do when deciding between these systems is to consider the type of conditions you want to drive in. Four-wheel drive systems are popular with serious off-road drivers and farmers. All-wheel drive has gained popularity with people who simply want an automatic increase in traction when road conditions require it, like when they’re doing a South Island road trip in winter. However for many people who typically drive in normal road conditions, the added purchase, fuel and maintenance costs of 4WD and AWD vehicles can make sticking with 2WD an attractive proposition.
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