AWD vs 4WD
Considering all-wheel drive or four-wheel drive? Great. But why, and what’s the difference?
If you’re venturing out of town and away from the tarmac you could probably do with some clever technology to help you out. Here’s how it works.
A horse that only canters on two legs, while quite interesting to watch, wouldn’t actually be of much use on the Olympics cross-country course. Likewise, an SUV that only ever uses two wheels wouldn’t take you very far into the forests and mountains of this fair country.
When you have a recreational lifestyle that means the tarmac runs out before you get to where you need to be – or if wet roads are a regular reality – an SUV with all of its wheels seeking traction is more than just a safety benefit, it’s a necessity.
But what’s the difference between all-wheel drive (AWD) and four-wheel drive (4WD) and does it really matter?
First, we’ll answer the latter part of the question, and the answer is: it depends. It depends on what you’re doing and where you’re going. It’s mainly a matter of terminology and intended use – a 4WD is perceived as one that is more likely to see rough terrain. If you want a genuine off-road experience just for the sake of it, if tackling mud and rocks and bogs is the end goal, then you need 4WD with a few tricks like low range gearing – which you can’t get in an AWD vehicle.
Some SUVS offer permanent 4WD (very similar to AWD) while others provide it part-time, when selected – if you mostly drive on the road and want to choose when to power all the wheels (for fuel economy, perhaps) the latter is a valid option.
Most 80 Series Land Cruisers are full-time 4WD. Power goes to all four wheels to maximise traction, and, if there’s any wheel slip, drive is still happening at the other wheels (although when a wheel spins and the vehicle stops moving, all the power goes to that wheel, meaning the other wheel on the axle won’t move unless there’s some form of locking differential). In the Land Cruiser 80 there are three differentials, one on each axle and one in the centre of the vehicle, in the transfer case.
In general terms, a differential allows wheels to rotate at different rates, which can be a problem off-road but is essential when driving in normal conditions. When you’re turning, for example, the outside wheels have to travel further and therefore faster than the inside ones, yet you still want equal drive to both wheels; if there was no differential you’d be skipping all over the place without traction and wrecking your axle and possibly a whole lot of other important bits connected to it. A centre differential means the front and rear axles turn at different rates when encountering corners and different levels of traction, and this is why a locking or lockable centre differential is essential off-road.
A locking centre differential (whether manual or automatic) allows the two axles to turn at the same
rate, meaning that if there is traction at one axle and not the other the vehicle will keep moving. Some 4WDS have the added ability to lock the axle differentials for extra traction, or these can be fitted.
In some modern 4WDS the computer senses wheel slip and automatically – some say instantly – sends torque to the other wheels via the traction control/abs system (torque is basically the twisting, pulling power of the wheel). The spinning wheel is thus isolated and progress is maintained. Vehicles like this often have a locking centre differential and some, such as the Land Rover Discovery and Mercedes G-class, also have an axle locking differential or two for added capability.
A more off-road biased 4WD SUV might have low range gearing, which provides maximum torque at low speeds when traction and/or obstacles are an issue (usually there are two gears lower than normal first gear). Generally, all-wheeldrive vehicles don’t have this feature.
Ever-popular in NZ, Suzuki has manufactured SUVS with low range gearing for years, and there are loads of nimble, lightweight and eminently capable Sj/samurais and Jimnys out there in the wilderness. The Grand Vitara also comes with a low range gearbox, which is a massive plus when the going gets tougher on the way up to the ski field, for example. Launching and retrieving a boat at the beach with a Grand Vitara, as a neighbour of mine does every weekend, is significantly easier in low range, allowing more high torque, low-speed grunt as well as more control over the direction of the trailer.
For a long time, Subaru marketed its all-wheel-drive cars using The Motels’ song ‘Total Control’ in their advertising. And that’s the idea behind AWD technology: there’s more grip on the road with all wheels driven, less chance of losing traction and control. I still regret selling my AWD Legacy because I could always pull away in the wet with no wheel slip.
I would argue that AWD is of considerable benefit for off-tarmac conditions. Most AWD vehicles will have some form of limited slip centre differential, and this basically means the two axles find it a bit harder to turn at different speeds, and so when traction is lost there could still be some drive to the wheels with grip.
So it’s really over to you and where you want to go. If it was me, I’d have as much capability as possible because it means I could go wherever I wanted to – there’s potential. These vehicles are built with adventure in mind, and most of them, regardless of their off-road systems, are designed to get you out into the world beyond the ordinary.