CarWale Gyan: All-Wheel Drive (AWD) and Four-Wheel Drive (4WD)

Introduction

You might be thinking what is the difference between an All-Wheel Drive (AWD) and a Four-Wheel Drive (4WD). In both types, the engine drives all four wheels so in one sense there is no difference, right? We are here to change that perception for there is a difference between these two terms and they aren't really interchangeable with each other.

Now, AWD is commonly used in cars that jave all the wheels running at all times. On the other hand, a 4WD is a generally accepted term for a car that uses a driver-selectable system that mechanically engages the drive to all four wheels, and otherwise has provision to be driven on 2WD.

AWD - All Wheel Drive

AWD - As the name implies, all-wheel-drive systems power both the front and rear wheels, all the time. But in practice, two types of drivetrains are called AWD. One drives all the wheels continuously and some manufacturers prefer to call this as full-time AWD. The second, often called part-time AWD or automatic AWD, operates most of the time in two-wheel-drive mode, with power delivered to all four wheels only when additional traction control is needed.

Why we need AWD?

In a 4WD system, power is sent to all four-wheel equally, so each wheel spins at the same constant speed. While this helps in straight line driving, or off-roading through low-traction surfaces, it isn’t ideal for driving where there’s ample traction – like tarmac or concrete roads. And it is also difficult to turn a vehicle into a corner since all the wheels are rotating at same speed instead of having relative motion between them. Therefore, AWD varies the amount of power sent to each wheel – either mechanically or electronically – thus providing ease of driving in both on- and off-road condition.

Advantages and disadvantages of AWD

The best thing about AWD is that the driver doesn't have to make any decisions about engaging the system. Either all the wheels are being driven full time, or the system itself is designed to sense a loss of traction and send power where it's needed. While AWD can work well in a variety of conditions, from rain to snow to light off-roading, it's generally considered a lesser choice by serious off-roaders. Also, the AWD increases the cost of a vehicle and, in most cases, it has a reduced fuel economy compared to a 2WD vehicle.

4WD - Four Wheel Drive

4WD - This is the more traditional system that delivers torque through a series of the front, rear and central differentials, transfer cases and couplings, which allow the vehicle to operate at maximum traction under a variety of conditions. Compared to AWD, the 4WD systems are more robust and can generally handle more rugged terrain. Many 4WD systems also have low and high range gearbox that can be selected by the driver, either with an electronic switch or a mechanical lever. The low setting provides maximum traction in off-road driving, while the high setting is the default configuration, useful for slippery on-road conditions, such as snow, ice, loose sand or gravel.

Why we need 4WD?

A four-wheel-drive system is capable of sending a fixed amount of power to each axle, and it can be controlled by the driver using a limited-slip differential (LSD). Therefore, whichever tyre has the most amount of traction gets the power it requires thus prevent the vehicle from getting stuck. Moreover, in regular road use, the 4WD can be operated in a two-wheel-drive mode.

Advantages and disadvantages of 4WD

4WD vehicles are generally best at handling adverse conditions, both on-road and off it. These days, the 4WD design has become increasingly refined as well. But, depending on the make and model, 4WD still often delivers a stiffer ride than 2WD. These systems also have a detrimental effect on fuel economy and increase the cost of the vehicle - both initially and during maintenance

Conclusion

So whether you would buy a 4WD or an AWD solely depends on your daily driving conditions. For serious off-roaders, a proper 4WD vehicle is an ideal choice, for everyone else, a simple yet intelligent AWD system will suffice.