Most people refer to any large SUV that looks like it was designed to go off-road as a ‘4×4’. However, a ‘4×4’ is really any four-wheeled vehicle that supplies power to all four wheels to drive the vehicle forward.
4x4s come in two different drive-train styles, all-wheel drive and four-wheel drive. Therefore when it comes to choosing a 4×4 that can tow your boat or caravan, or just something to keep up with your mates out in the bush, you’ll be faced with the tough decision of choosing between the two.
Each type is suited to particular conditions and they also share a few similarities.
So how do you know which is the right one for you?
In this guide, we will discuss the key differences between 4WD and AWD systems, as well as some considerations to help you choose the right type for your needs.
What is a 4WD vehicle?
Typically, larger SUVs and utes with four-wheel drive have a lot more torque (the turning power of an engine) than regular cars. This makes them far more suitable for pulling heavy loads. Most 4WDs have been designed to intentionally leave the bitumen in a cloud of dust and dirt.
However, the addition of 4WD usually makes these vehicles a lot heavier than other on-road vehicles, negatively impacting fuel economy.
A 4WD vehicle uses two differentials (a mechanism that allows a pair of wheels to spin at different speeds) on either axle of the vehicle. This allows for an exact 50/50 split of power to be distributed to each one. They typically feature two modes; 4L (low-range mode) and 4H (high-range mode).
4H is used for day-to-day driving. It features a taller gear ratio which puts less strain on the vehicle’s drivetrain. 4L on the other hand, features a far smaller gear ratio and is designed for low-speed off-roading where you need that extra torque to climb steep hills or cross heavily congregated terrain.
4WD drivetrain systems come in two different variations, part-time 4WD and full-time 4WD.
How does a part-time 4WD work?
Part-time 4WD allows you to choose when your vehicle operates in 4WD or 2WD mode. 2WD mode is used when traveling on the bitumen, while 4WD mode is engaged when the terrain gets bumpy or you need added traction. To make the transition, part-time 4WDs must either mechanically or electronically engage the front driveshaft.
This is done through a device called a ‘transfer case’, which is designed to evenly distribute torque between the front and rear drive shafts. This maximises the output at each wheel for towing and driving off-road. The main difference between part-time and full-time 4WDs, is that full-time 4WDs use a differential to control the wheel speeds instead.
However, engaging the transfer case ‘locks’ all four wheels, which forces them to travel at the same speed. This system is very similar to when a full-time 4WD has their differential lockers engaged.
Making all the wheels spin at the same speed, can create a lot of additional traction. However, that energy is forced back into the axle and the drivetrain if engaged in the wrong circumstances.
Engaging the transfer case makes it pretty dangerous when cornering at high speeds, while also putting a huge amount of stress on the transmission. This may eventually cause it to seize which is often referred to as ‘wind-up’. This is the main reason why part-time 4WDs must remain in 2WD while travelling on the road.
Common part-time 4WDs include: Jeep Wrangler, Nissan Patrol GU, Toyota FJ Cruiser and most dual-cab 4X4s (eg. Ford Ranger and Toyota Hilux).
Part-time 4WD pros
- Adequate off-road abilities
- 2WD is far more economical to drive than 4WD
- Lighter than a full-time 4WD system
Part-time 4WD cons
- Far less traction when 2WD is engaged
- Greater burden on electronics including stability control and traction control when 4WD mode is engaged
How does a full-time 4WD work?
Without going into too much technical detail, a centre differential allows the front and rear differentials to rotate the axles at different speeds, meaning when you turn, the inside wheels rotate slower than the outside wheels. This also prevents a nasty wind-up in the transmission if the wheels were to all travel at the same speeds.
Most 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 all 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 when engaged in 4WD mode.
Common full-time 4WDs include: Toyota Prado, Toyota Landcruiser 200 Series, Mitsubishi Triton, Volkswagen Amarok, Ford Everest and Land Rover Defender
Full-time 4WD pros
- Performs better than a ‘locked’ part-time 4WD off-road
- 4L is extremely powerful and provides great torque
- Tried and true system that has worked for a long time
Full-time 4WD cons
- Heavy and sluggish on the road
- Reduced fuel economy
- More moving parts to go wrong
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. For example, if the internal computer detects that the rear wheels are slipping, more power can be automatically supplied to them to regain traction.
However, an AWD system cannot apply the same amount of power to the wheels as a 4WD in 4L. They also do not feature a ‘differential locker’, the device needed to ‘lock’ each axle into spinning at the same speeds. This makes them far less capable of serious off-roading.
How does AWD work?
AWD systems are designed to ‘work on the fly’, rather than be restricted to a set ratio the wheels have to spin at like a 4WD system.
AWD vehicles use sensors in the front, centre and rear differentials to detect when a wheel loses traction. The drivetrain system then automatically diverts power to the wheel with the least traction at that moment, optimising performance and regaining traction on the road.
Common AWD vehicles include: Subaru Forester, Subaru Outback, Mazda CX-5 Touring, Kia Sportage and Audi A4.
- 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
- Relies heavily on electronics to function properly
4WD vs. AWD – which is for me?
When deciding what type of drivetrain you need your future 4×4 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 4×4 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 4×4?
- 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.
In general, if you are choosing between the two drivetrain systems, AWD is used for very light off-roading and driving for the majority of times on sealed roads. This is due to AWD systems not having the ‘low-range’ gearing like a 4WD or the ability to ‘lock’ the system, which makes them unsuitable for serious off-roading. That being said, gravel, light snow, rain and other varying terrains won’t hinder it’s abilities.
On the other hand, a 4WD system is crucial if you plan on going on anything more than a dirt road or plan on towing a heavy trailer. If you are towing a boat in particular, a 4WD with 4L is crucial for keeping traction on slippery boat ramps.
It is also worth considering what you may be using the vehicle for in the future. Even though currently you are touring the countryside on sealed roads, if you plan on doing more outback adventures with an off-road camper trailer, it may be worth buying a 4WD, to begin with than having to sell your current AWD vehicle when your priorities change.
As you can see, choosing a 4×4 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.
Photos provided by us and Chris Howey/Shutterstock.com
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