AA Buyer's Guide: 4WD versus AWD, what's the diff?
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Kiwis are buying more All-Wheel Drive (AWD) and Four-Wheel Drive (4WD) vehicles than ever before.
This is partly due to widespread availability, but also due to the latest advances in drivetrain technology which make running these systems a lot more efficient and effective than ever before.
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 them.
If you live out of town, you may be looking towards a more capable vehicle with either 4WD or AWD technology. Typically, 4WD is targeted more towards frequent off-road drivers, whereas AWD is more for if you only occasionally head off the beaten track.
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, which affect the operation of the drivetrain depending on the conditions that are encountered.
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 up the centre differential and restricts any rotational difference between the front and rear axles. This is a feature commonly used when off-roading to gain maximum traction.
Just like with full-time 4WD, the driver has the ability to change the way the vehicle behaves. If you’re driving to the local dairy 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 part-time 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 two-wheel-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’s hybrid AWD system was showcased on the new RAV4 when it was released last year and has been available on Lexus models for many years. The hybrid system is responsible for distributing power to the rear wheels via an electric motor, this means that the rear wheels are not directly connected to the engine. The RAV4 Hybrid’s power management computer determines exactly when rear traction is needed, otherwise it saves fuel by diverting all power to the front wheels instead. The electric motor on the rear axle can produce a maximum of 121Nm of torque.