Many people think that the terms 4WD and AWD are interchangeable, but in fact, these two systems are quite different.
4WD stands for four-wheel drive and refers to a vehicle—often an SUV (Sports Utility Vehicle)—which uses a driver-selectable system that mechanically engages the drive to all four wheels. AWD, on the other hand, stands for all-wheel drive and refers to a vehicle that drives all of its wheels all of the time.
4WD
A 4WD vehicle is designed for off-road situations because of the extra traction it provides in difficult terrain. A 4WD or 4X4 vehicle typically has a truck-based platform with oversized wheels, special off-road tyres, and a manually selected and locked 4WD driveline.
When 4WD is selected, what is known as the transfer case divides power between the front and rear axles, applying the maximum amount of torque to each wheel. However, this creates a problem when turning, as the inside wheels turn slower than the outside wheels, causing them to spin freely and lose traction. Modern 4WDs solve this issue with a ‘High’ setting, which splits the power less evenly between the inside and outside wheels, reducing slippage.
AWD
An AWD vehicle drives all of the wheels all of the time, with the added advantage of a limited-slip differential or electronically controlled clutch. This allows for a rotational difference between the front and rear axles. The system provides twice the grip of a driver-selected 4WD system because it is always engaged, making it safer in slippery road conditions or when extra traction is needed.
The biggest difference between 4WD and AWD is that the AWD system is engaged all the time, whereas the 4WD system must be manually selected. Modern AWD systems are computer-driven, with sensors on each wheel monitoring traction and speed hundreds or even thousands of times per second. An ECU (electronic control unit) determines which wheel gets the power based on which one has the most grip.
Pros and Cons of Each
Both 4WD and AWD systems have their own advantages and disadvantages.
4WD Pros and Cons
- It offers greater traction in low-speed off-road conditions.
- Since it’s a selectable system, it can be turned off in normal driving conditions to improve fuel efficiency.
- However, it adds weight and complexity to the vehicle, increasing both the purchase price and running costs.
AWD Pros and Cons
- It provides improved grip and control all the time and in all road conditions.
- It can be fitted to a wide range of vehicles, enhancing traction and handling.
- However, its permanently engaged system reduces fuel economy.
Which to Choose?
Both systems have their benefits and drawbacks, so how do you decide which is right for you? It depends on what you plan to use the vehicle for.
If you’re an avid off-roader, a 4WD with its rugged construction and superior traction is likely the better choice. Keep in mind, however, that 4WDs tend to have higher costs due to oversized wheels, off-road tyres, and more frequent maintenance. You’ll need to be prepared to pay more for the privilege of being able to take your vehicle just about anywhere.
On the other hand, if you live in an area with bad weather or simply want a safer car for road driving (and occasional off-roading), an AWD might be the better option for you.
Whichever you choose, hopefully this article has clarified the difference between AWD and 4WD, so when a salesperson tries to tell you they’re the same thing, you can set them straight.
