BUYER’S GUIDE
What’s the difference between AWDs and 4WDs?
Kiwis are buying more allwheel drive (AWD) and four-wheel drive (4WD) vehicles than before.
This is partly due to widespread availability, but also because of the latest advances in drivetrain technology which make running these systems a lot more efficient and effective.
But why do manufacturers use different terms? Isn’t AWD and 4WD the same thing? We regularly answer this question for our AA members, who are trying to ascertain which system would best suit their lifestyle.
Full-time 4WD
Full-time 4WD, as the name suggests, is a system where torque is delivered to all four wheels evenly, all of the time. The driver usually has several options available that affect the operation of the drivetrain depending on the conditions.
Under regular driving conditions (around town), the front and rear axles are split by a differential which lets the wheels operate at different speeds when required — such as going around corners.
In most vehicles, you’ll also have the option of diff lock. This locks the centre differential and restricts any rotational difference between the front and rear axles. This is a feature commonly used when offroading to gain maximum traction.
Part-time 4WD
Just like with full-time 4WD, the driver has the ability to change the way the vehicle behaves. If you’re driving to the supermarket, then power to two wheels is more than enough. But if you occasionally plan to take your vehicle off the beaten track, then you have the option of selecting 4WD mode whether by mechanical or electronic means.
It’s important to note that because these part-time systems might not have a centre differential, we advise not driving the vehicle in 4WD on regular tarmac as this can put stress on the drivetrain.
All-wheel drive (AWD)
AWD is a little more complicated. It works automatically to send torque to all four wheels, but only when the car senses extra traction is required, such as on a slippery surface.
In many situations, the AWD system will only be working parttime through a viscous coupling or electromagnetic clutch. This clutch allows the vehicle to have more control over where the wheels are powered.
Like any 4WD system, a disadvantage of AWD is that it’s more expensive than a two-wheel drive drivetrain and added friction between the tyres and road as well as frictional losses in the transmission system leads to increased fuel use.
AWD grip is only as good as the car’s tyres, and it won’t necessarily be that much safer than a twowheel-drive variant in everyday conditions.
Next time you’re on the hunt for a vehicle, think about your driving requirements before committing to an AWD or 4WD vehicle. Remember that regardless of which four-wheel system you choose, there will be additional maintenance requirements as well as increased fuel costs.
The future of AWD
The AWD systems in Tesla’s premium ‘D’ (dual-motor) models feature motors at each end of the vehicle, and require no physical driveshaft linking the front and rear axles.
This system adapts to the grip on the road to distribute available horsepower, maximising both torque and power.
This technology helps these specific Tesla models accelerate faster than most supercars.
Toyota will also offer AWD in some of its hybrids later this year — it will be available as an option on the popular Prius and RAV4 models.