What's the difference between AWD and 4WD?
The rise and rise of all-wheel-drive and 4WD vehicles goes on as more manufacturers see the benefit of these drivetrains in terms of performance and safety.
So, what’s the difference? They both mean the power’s going to all the wheels, right?
Well yes … and no. As so often is the case in modern motoring, the answer isn’t always cut and dried.
Once upon a time it was pretty simple.
Four-wheel-drive meant you could select to have the drive going to either two wheels or four.
Usually a form of locking hub was required so the power would go to the usually non-driving wheel, the front wheels, and this was pretty much the domain of off-road vehicles like Land Rovers and Land Cruisers.
Meanwhile, all-wheel-drive vehicles were just that – all the wheels got all the power all the time.
Naturally, it wasn’t quite as easy as that, considering a vehicle needs to corner, so centre diffs and other wizard bits of kit were involved to ensure that happened.
Now, while the above could be used to simply explain the difference, there are a few variables, not helped by individual manufacturer’s use of terms to describe their vehicles’ drivetrains.
So, to keep this simple and prevent us all losing more hair than necessary, let’s divide it all into three styles – full-time 4WD, part-time 4WD and all-wheel-drive (AWD).
Just like it sounds, full-time 4WD means that at all times power is going to all four wheels.
There are often several options then available to the operator depending on road conditions and most have a centre differential lock.
When driving on sealed surfaces, the front and back axles are split by a differential so the axles can spin at different rates as required, such as when cornering.
With the diff lock engaged, the axles and therefore wheels turn at the same rate, maximising traction.
Some also offer low range, with a much lower gearing for crawling out of, or indeed into, sticky situations.
Part-time 4WD is the original and most basic of these styles of drivetrains and is pretty much as described above – torque is supplied to two driving wheels, just like any 2WD system, but drivers have the option to engage power to the other two wheels for more traction.
These systems usually do not have a centre diff so really, engaging four-wheel-drive is for off-road driving only.
AWD vehicles also have torque going to all the wheels all the time, and don’t often have options such as low range or locking centre diffs.
Their centre diffs, however, usually have the ability to limit slip between the axles if grip becomes an issue at the wheels.
Right, now that’s all clear here’s another question. Do we need all that malarkey?
Yes, we do indeed, as each one of the above has applications the other can’t handle as well.
For instance, a high-performance vehicle gains great advantage from an AWD system in terms of performance and handling, but would not from a 4WD system.
Likewise, vehicles designed for serious off-road use need the flexibility, and ability to handle high-torque situations such driving throws up, that 4WD offers.
It truly is a case of horses for courses, or in this case, drive trains for driving aims.
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Lindsay Saunders has been writing, editing and producing words and photos for more than three decades, starting back when he drove a 1971 VW Type 3 fastback.
Now he’s got a Hyundai I30 diesel, a 1999 LWB Hi-Ace (camper project) and wishes his wife’s EJ Holden station wagon was actually his.