New Zealanders are buying more all-wheel drive (AWD) and four-wheel drive (4WD) vehicles than before — partly because of widespread availability, and partly because the latest advances in drivetrain technology are making running all- or four-wheel drive more efficient and effective.
But why do manufacturers use different terms? Isn’t 4WD and AWD the same thing? We often get questions from AA members about which system will suit their lifestyle, so let’s break it down.
Fulltime 4WD
Full time 4WD is a system where torque is delivered to all four wheels evenly and constantly. The driver usually has several drivetrain options, 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 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. It is a feature commonly used when off-roading to gain maximum traction.
Part-time 4WD
Just like fulltime 4WD, the driver has the ability to change the way the vehicle behaves. If you’re getting groceries with the kids, then power to two wheels is more than enough.
But, if you plan to head down Ninety Mile Beach, you have the option of selecting 4WD mode by mechanical or electronic means.
It’s important to note that because these part-time systems may not have a centre differential, we advise against driving in 4WD on regular tarmac as this can put stress on the drivetrain.
All-wheel drive (AWD)
All-wheel drive is relatively recent innovation and a little more complicated. It works automatically to send torque to all four wheels only when the car senses extra traction is required.
In many situations, the AWD system will be working only 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, with electronic stability control mandatory in all new cars, 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.