When purchasing a new vehicle, many consumers may question the benefit of buying an All-Wheel Drive when their driving is primarily in the city, and wonder if this is a function they really need?
The short answer is yes. AWD vehicles offer significant safety benefits to city drivers and consistently perform better in the city than other cars for a range of reasons. The safety benefits are dependent on the type of All-Wheel Drive system used in the car. There are basically three main categories: AWD, Part-Time AWD and Four Wheel Drive (4WD).
A true AWD car has far more safety benefits in the city than a Part Time AWD or 4WD vehicle. Understanding how an AWD operates differently to Part Time AWD and 4WD vehicles is important in order to understand the safety benefits an AWD provides.
Cars are measured on an active safety point of view, which is the ability of the vehicle to assist the driver to avoid an accident.
On this basis, 4WD vehicles have little to offer city drivers. 4WD vehicles are generally based on heavy truck platforms that use a manual 4WD system. Manually selected 4WD systems cannot be selected when driving on city streets and fuel consumption is generally higher. Read more about the difference between AWD and 4WD.
Some so-called AWD vehicles are actually only part time AWD. These vehicles switch to AWD when traction is lost on the primary drive axle. This means that stability and directional control can be lost before the AWD system activates, which effectively means part time AWD vehicles are in fact two-wheel drive at the time that most counts.
A true All-Wheel Drive vehicle drives on all four wheels all of the time, regardless of the type road surface or how the AWD vehicle is being used.
The key benefit of this is safety. A true AWD vehicle, such as Subaru Symmetrical All-Wheel Drive, always has twice the grip capacity to generate forward momentum. This is a significant safety benefit, because it means the stability and degree of driver control is greater than a rear wheel drive, front wheel drive or part time AWD car of the same weight and tyre configuration when under drive power.
This safety benefit is crucial when the level of traction is low, which often occurs in the city on a wet and rainy day. This happens due to the build up of grease, grime and oil on the surface of city streets. On wet, rainy days, particularly after an extended dry period, it becomes extremely easy to lose traction when accelerating, which causes wheel spin. This usually happens when drivers accelerate at busy intersections or to overtake turning cars, and drivers quickly lose control.
However, because a true AWD car drives on all four wheels all of the time, the drive force is more evenly distributed across the four wheels, offering twice the amount of grip. The result is a safer, more stable and reliable acceleration of the vehicle, because in this situation the grip of the best true all wheel drive car is twice that of the best two-wheel drive car.
In the safety stakes, a true AWD vehicle also outperforms the other categories in the city when it comes to cornering under drive power. In an AWD vehicle, each tyre transmits half the total drive force compared to a two-wheel drive car. Because the two-wheel drive car axle then has to transmit twice the forces of the AWD car, the two-wheel drive has less grip available for cornering forces.
This means that if the engine power increases at any point, the two-wheel drive car uses up more of the available grip, which can leave insufficient grip to deal with cornering forces. When this happens, the tyre will lose traction and slip sideways. The car will slide on the drive axle, in what is known as an understeer or oversteer manoeuvre. When the drive axle loses cornering traction, directional control is also lost.
This is not the case for the true AWD vehicle. Because the AWD only transmits half the drive force on each wheel, it has greater grip available for cornering forces on the drive axle. The AWD can, therefore, withstand much higher cornering forces than the best two-wheel drive car. This is particularly important in slippery conditions, like driving in rain and heavy city traffic, where grip is reduced and cars are driving close to other obstacles. Any loss of directional stability can easily result in impact with other vehicles or roadside obstacles.
A true AWD car, therefore, offer drivers significant safety benefits in the city, because the car provides the driver with a higher level of control, and subsequently a better ability to avoid potential accidents, even at low speeds when the level of traction is poor.