21 May 2018
Kiwis are buying more All-Wheel Drive (AWD) and Four-Wheel Drive (4WD) vehicles than ever before– partly because of widespread availability, and partly because the latest advances in drivetrain technology is making running all or four-wheel drive more efficient and effective than ever.
But why do manufacturers use different terms? Isn’t 4WD and AWD the same thing? AA Members are often querying the differences and trying to ascertain which system will suit their lifestyle better. So let’s break it down…
Fulltime 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 to them 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.
Part time 4WD
Just like with fulltime 4WD the driver has the ability to change the way the vehicle behaves. If you’re doing the groceries with the kids, then power to two wheel s is more than enough, but if you plan to head down Ninety Mile Beach, 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)
All-Wheel Drive is a much more recent innovation and is a little more complicated. It works automatically to send torque to all four wheels only when the car senses extra traction is required, such as 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 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 /4WD vehicle. Remember that regardless of which four wheel system you choose, there will be additional maintenance requirements as well as increased fuel costs.
