EVER WONDERED WHAT the difference is between all-wheel drive (AWD) and four-wheel drive (4WD)? No? Well, we are going to tell you anyway.
It used to be easy to differentiate between AWD and 4WD. AWD was for sporty cars on tarmac roads – think Audi’s quattro system on the R8 – and 4WD was for trucks and SUVs on mountainous passes. Think Land Rover Defender. So, AWD for on the road and 4WD for off the road.
But nowadays the lines are getting blurred, new systems are being developed all the time and the terminology is sometimes used interchangeably. But roughly, you can break the systems into four: full AWD, part-time AWD, full 4WD and part-time 4WD. The difference is how and when torque is supplied to each wheel.
According to the YourMechanic website:
In the US, in order for a vehicle to be labeled All-Wheel Drive, both axles must be able to receive power and rotate at different speeds simultaneously. If a vehicle has a transfer case, meaning that if both axles are receiving power then they will be forced to spin at the same speed, then it is Four-Wheel Drive, not All-Wheel Drive.
Traditionally, four-wheel drive systems use a series of differentials, one for the front axle and one for the rear with a transfer case in the middle. This allows the front and rear wheels to operate at different speeds when required, when cornering for example.
Part-time systems work in two-wheel mode until the driver or an onboard computer turns on the 4WD system so all four wheels share the load. When 4WD is engaged the transfer case locks the front driveshaft to the rear driveshaft, so each axle receives half of the torque coming from the engine. For a more technical explanation with diagrams check out this How Stuff Works article.
Most 4WD systems have a high and low setting with the low setting supplying even greater amounts of torque for pulling or climbing in an off-road setting or for descending a steep uneven slope. The high setting is usually used for slippy and icy surfaces or loose gravel and sand.
Full-time AWD systems use a front, rear and centre differential to provide power to all four wheels of a vehicle at all times.
Part-time AWD operates like the part-time 4WD systems, in that it works in two-wheel mode until the car senses it is time to send power to all four wheels. However, it does this automatically so there is no high or low setting and no need for the driver to turn on the system.
Some AWD systems also employ torque vectoring in which power is sent to the wheels with most traction no matter what side of the car they are on.
AWD and 4WD can help vehicles accelerate quicker and more smoothly and can help with traction in slippy conditions. But these systems are more expensive, add more weight, increase fuel consumption and are more costly to repair.
So do you really need a car with AWD or 4WD?
If you plan on getting properly off-road a lot of the time, then a vehicle with four-wheel drive is probably the better option for you. 4WD features on pick-ups and SUVs with truck-based platforms as these are durable vehicles that can match the rugged 4WD system.
If you don’t go off road much but live somewhere that experiences a lot of wintery and icy conditions then a car with a sophisticated all-wheel drive system may be the right choice for you as the car responds to the terrain and conditions instantly without you having to do anything.
For most of use though living here in Ireland a two-wheel-drive system with traction control and a good pair of winter tyres is all we’ll ever need.
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