What’s the “diff”? – 4WD and AWD explained

There is a reason why All-Wheel Drive and 4-Wheel Drive don’t share the same name.

With the numerous drivetrains out there, it is no surprise that even the best of car guys throw the terms AWD (All-Wheel Drive) and 4WD (Four-Wheel Drive/ 4×4) haphazardly around without knowing the difference between the two. I get it; I used to be guilty of this as well. If a car has 4 wheels in total, then doesn’t that mean that AWD is 4WD? Well, not exactly.

They do have similar results though, which is to provide the best traction to the vehicle in tough conditions. But how those results are achieved is what separates the two.

Before we can go any further in explaining how AWD works, we have to understand a bit about the Ackerman Principle. During a turn, all 4 wheels spin at a different rate because of different angular velocities. Between the outer and inner tires, the outer tires spin the quickest and between the front and rear tires, the front moves the quickest. To maximize grip on all 4 tires, they all have to be allowed to spin at different rates. Otherwise, understeering and buckling will occur.

 

4WD – Four-Wheel Drive

Four-Wheel Drive (4WD) is the oldest between the two systems and is more commonly found on SUVs and trucks.As the name implies, 4WD is a drivetrain that sends power to all 4 wheels to provide maximum traction. 4WD is generally activated by the driver either via buttons or a separate transfer gear lever with notches or gates for 2WD High Range (2H), 4WD High Range (4H) and 4WD Low Range (4L).

2H is the default setting for paved roads because it keeps the front wheels free while driving power to the rear. This setting will usually be the default of the transfer case because it maximizes maneuverability and fuel efficiency for city driving in ideal conditions and doesn’t wear out your front tires as quickly.

4H is best when you are running in relatively high speed yet traction is needed to handle slippery conditions. So whether you’re on soft, wet, muddy, or icy roads (not in the Philippines, of course), this is the best setting to use. Sometimes it can be used for highway driving in the rain, but it is best to check the owner’s manual to see if the vehicle can run at around 100 km/h with 4H.

4L is the setting for when things get really tough. 4L prioritizes low speed, high torque off-roading; meaning you’re probably on a trail with boulders, rocks, heavy mud, steep inclines, and river crossings. Any vehicle with 4L engaged can only be driven at a crawl. Some even use limited slip differentials to give the driver maximum traction and control.

4WD depends a lot on driver discretion and experience, and is also designed and engineered to handle tougher tasks and rougher terrain; such is why 4WD is more common in body-on-frame SUVs (i.e. PPVs). While AWD is similar, it’s a completely different species once you start looking its capabilities and purpose.

 

AWD – All-Wheel Drive

All-Wheel Drive is a fairly recent technology usually found in cars ranging from city trotters to high performance vehicles because of its application, which has more to do with grip than with off-road capability. Versus RWD (Rear-Wheel Drive) and FWD (Front-Wheel Drive), AWD theoretically has better grip because power is properly sent to all wheels properly and efficiently based on the Ackerman Principle.

Generally-speaking, AWD vehicles are either biased towards FWD or RWD, with automated electronic systems and transfer mechanisms that sends power to all four wheels when it senses a loss of traction. The AWD system can also be either manually engaged (usually via a lock button) or not at all, making it permanent all-wheel drive.

What sets AWD systems apart are the use of complex systems to allow wheels to be driven on an as needed basis through the use of electronically-activated clutches and differentials, otherwise known as torque vectoring. This allows it to be used for high performance applications since the AWD system computes the best way to deliver power whether it is on a straight or taking a tight turn.

To an extent AWD is like 4WD, but allows all wheels (that is why it is called AWD) to move at independent rates for maximum grip and effect. Lately manufacturers have been taking the technologies used in AWD and applying them to more classic 4WD applications, creating a veritable hybrid 4WD drivetrain that combines the best of both.

 

Knowing all this, a better understanding on the different systems not only allows us to make a more informative choice when buying a vehicle with any of these systems, it also helps us maximize them for a better driving experience. At the very least, now you have a good topic to talk about with your fellow gearheads.

 

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Deputy Editor