Being an avid outdoor enthusiast, the places you love to explore are, by definition, a bit difficult to get to. And let’s be honest, you’ve probably got quite a lot of gear to take with you as well.
Let’s just say your garage is well organised, but…full.
These are just two of the many reasons why AWD and 4WD vehicles are the vehicle of choice for the Australian weekend warrior: they’ve got the boot space for the gear and the grunt to get it to your destination.
But if you’re searching for the perfect adventure vehicle, you might be wondering, ' just what is the difference between all-wheel drive and four-wheel drive systems, and which is best for me?'
To make an informed decision, you’re first going to need a clear understanding of the way these drive systems work and how they perform driving on different terrain.
So let’s kick things into low gear and take a look at all-wheel drive and four-wheel drive systems in more detail.
Photo: Scott Ivey. Scott's confident in his Pathfinder on the Cooloola Coast.
4WD vs. AWD – the same but different
AWD and 4WD systems are very similar; that’s a big part of the reason why the terms are frequently used interchangeably, creating confusion around how they actually differ.
To make matters worse, we also often refer to large SUVs designed to go off-road as 4x4s.
But a 4x4 is really any four-wheeled vehicle that supplies power to all four wheels to drive the vehicle forward. So technically, an AWD vehicle is a 4x4 as well.
All set with your 4x4? Check out the full range of 4WD accessories and gear at our marketplace.
What is a 4WD vehicle?
Typically, larger SUVs and utes with four-wheel drive have a lot more torque than regular cars. 4WDs are designed to intentionally leave the bitumen in a cloud of dust and dirt.
With the option to switch to low-range mode (4L), a 4WD system maximises torque output at all four wheels. In 4L, 4WDs are great at towing and pulling heavy objects (e.g. boats, caravans, your mate’s 4WD that got stuck, etc.) and crawling over rugged terrain.
However, the addition of 4WD usually makes these vehicles a lot heavier than other on-road vehicles, negatively impacting fuel economy. And some systems (known as part-time 4WD) must remain in 2WD while driving on the road (we’ll explain why in a minute).
What is an AWD Vehicle?
Cars and larger SUVs featuring AWD, on the other hand, are best suited to driving on the road. An AWD system adjusts the level of torque supplied to all four wheels making them considerably better at driving in variable on-road conditions than regular 2WD cars.
And while some larger AWD vehicles can handle light off-road terrain, without 4L you won't be tackling any serious terrain (i.e. you definitely don’t want to try and cross the Simo in your Nissan Murano).
You'll need 4WD for sand this deep.
So in very simple terms:
On and off-road capable
4L (low range mode) provides maximum torque at all four wheels off-road
Heavy and sluggish on the road
Reduced fuel economy
Some models must run in 2WD on-road
Great performance in a range of on-road conditions
Drives all four wheels increasing torque and traction
No low-range (4L) capability
Very limited performance driving off-road.
So 4WD is better off-road and AWD is better on-road, but what exactly makes them better suited to different types of terrain? And what’s all this about some models only being 4WD, some of the time?
To answer these questions we are going to look at three 4x4 drivetrain systems in more detail:
Part-time four-wheel drive
Full-time four-wheel drive
How does part-time four-wheel drive work?
In the good old days, all four-wheel drives spent their time on the road as run-of-the-mill (slightly overweight) two-wheel drive vehicles. But when they left the tar-seal, they transformed into off-roading beasts capable of devouring even the toughest terrain.
Today, part-time 4WD systems are still used by vehicle manufacturers and are often favoured by serious off-road drivers.
When driving on-road, part-time 4WDs supply power to the rear axle only. Like a regular two-wheel drive car the front wheels are left to spin freely.
In the above graphic, you can see that while driving on-road only the rear driveshaft is being supplied with power.
To make the transition to off-road terrain, part-time 4WDs manually engage the front driveshaft. Today, this is done either mechanically or electronically.
When you engage 4WD, a mechanical device called a transfer case evenly distributes power between the front and rear drive shafts.
This transfers torque evenly to all four wheels via the front and rear axles maximising the output at each wheel for towing and driving off-road.
Why must part-time 4WD vehicles remain in 2WD on the road?
This is where things get a little more technical.
While a transfer case is essential for the even distribution of power between the front and rear axles, it also creates a problem when activated on the road; it locks all four wheels forcing them to travel at the same speed.
To demonstrate why this becomes an issue we need to understand the way cornering affects wheel speed.
Ever watched the sprints at the Olympics? Notice how the runner on the inside lane starts further back than the runner on the outside lane. That’s because the runner on the inside has a shorter distance to travel. The same principle applies to the wheels on a car.
When cornering, the inside wheels on the vehicle have less distance to travel than the outside wheels. If all four wheels are locked together, the inside wheels need to slip (lose traction) to keep up with those on the outside.
The outside wheels are travelling faster because they have further to travel in the time it takes to get from point A to point B around the corner.
Remember high school physics class? Speed = distance / time.
The sprinter on the left has less distance to travel than those on the right, similar to the inside wheels on a 4WD going round a corner.
On regular 2WD vehicles, this problem is solved by using a device called a differential which is installed between the driven wheels. The differential's job is to allow the inside wheels to travel slower than the outside wheels preventing wheel slip, providing optimum traction for cornering safely on roads.
On slippery surfaces like gravel, a vehicle with part-time 4WD engaged (locked wheels) can corner effectively because the inside wheels are able to slip to keep up with the outside wheels.
But, as we mentioned previously, modern roads and tyres are designed to maximise traction. More traction means it takes more torque to make a tyre slip, which in the case of cars driving on roads, is a good thing.
For a part-time 4WD, however, all that additional traction prevents the inside wheels from slipping; the energy generated is then forced back into the axle and the drivetrain. This makes it pretty dangerous when cornering and puts a huge amount of stress on the transmission eventually causing it to seize.
This is often referred to as wind-up and it’s the main reason why part-time 4WDs must remain in 2WD while travelling on the road.
Why would anyone choose a part-time 4WD?
All that is not to say that part-time 4WD systems are not worthy of your attention. In fact, many hardcore off-road drivers prefer part-time systems because of their simplicity and their potential for modification.
Modern part-time 4WDs also come standard with two off-road modes: high-range (4H) and low-range (4L).
4H drops the transmission into a lower gear range providing additional torque to all four wheels making it a good choice for driving on gravel or slippery conditions.
4L, on the other hand, multiplies torque output at each wheel by as much as 2.5 – 3x the normal amount! This is your go-to for serious off-roading – for climbing steep slopes and crawling over boulders.
This could go either way...
Contrary to what you might think, 4L is not always the best choice for driving on very slippery surfaces because the extra torque can cause the wheels to spin, digging your vehicle in deeper if you’re not careful.
Most part-time 4WDs will spend the majority of their time off-road in 4H, using 4L only when necessary.
So apart from them only working let’s say 20 hours a week, what else makes a part-time 4WD different from a full-time 4WD model? And if a transfer case prevents 4WD from being engaged safely on the road, how do full-time 4WDs overcome this?
The answers are in the diffs.
How does full-time 4WD work?
Part-time four-wheel drive vehicles are (usually) missing a key component that full-time 4WD systems have: a centre differential.
Without going into too much technical detail, a centre differential allows the front and rear drive-shafts to rotate at different speeds, similar to the way the rear diff allows the inside wheels to rotate slower than the outside wheels.
Combine a centre differential with front and rear diffs and you’ve allowed all four wheels to travel at different speeds while driving on the road, preventing that nasty wind-up in the transmission.
Some full-time 4WDs are designed for serious off-roading. To match the performance of a locked part-time 4WD system, they come equipped with a feature called differential lock.
A diff locker does exactly what its name suggests, it locks the centre differential forcing the wheels to travel at the same speed – regardless how much traction each wheel has at the time – making them perform more like a part-time 4WD off-road.
Full-time 4WDs also feature 4H and 4L modes like part-time systems, but cannot be driven in 2WD (hence the name).
How does AWD work?
That brings us to the modern all-wheel drive system. AWD is mostly used on vehicles that are designed to spend the majority of their time on the road — you won’t see any hardcore four-wheel drivers out there using an AWD vehicle.
The main reason for this is they are missing two key features need for off-roading: 4L mode, and a diff locker. Without these they won’t make it over those boulders or out of that mud, making them pretty useless in severe off-road conditions.
But, AWD (especially modern sophisticated systems) are great at adapting on the fly.
Some high-performance AWD vehicles use sensors in the differentials to detect when a wheel loses traction. The drivetrain system then switches between 2WD and 4WD, automatically diverting power to the wheel with the least traction at that moment, optimising performance, regaining traction on the road.
Which type of 4x4 vehicle should I choose?
When deciding what type of drivetrain you need your future 4x4 to have, the most important thing to consider is the full range of terrain you intend to explore.
Ask yourself questions like:
How will I use my 4x4 day to day? Will the majority of my driving be on-road?
What is the most extreme terrain that I expect to explore in my new 4x4?
Will I be towing a trailer, a caravan, or a boat?
Even if I’m not touring off-road today, would I like to be able to in the future?
Answering these questions will give you a good idea of what type of drivetrain you need your vehicle to have.
For example, if you’ve got your heart set on towing that shiny new Expanda Outback along the Cooloola Coast, a part-time or full-time 4WD system is going to enable you to experience and explore the full potential of that unique, challenging terrain.
Unfortunately, some destinations just aren’t accessible to an AWD vehicle.
But, if you’re looking for a vehicle to take the kids to the snow or an SUV that can handle the dirt roads out to your favourite free campsite; if you’re simply looking for more traction and safety features on-road, an AWD system might just be a great choice for you.
The reduction in weight means better fuel consumption, and on those long road trips with occasional dirt road sections, AWD vehicles really come into their own.
All-wheel drive vehicles are great at handling variable road conditions like rain, gravel, and even light snow.
As you can see, choosing a 4x4 is all about understanding how the available drivetrain systems handle different scenarios and deciding which system best aligns with where you want to go.
Now you know what to look for, it’s time to start searching for a vehicle that can take you to all the places you’ve always wanted to explore.