by Rob Callahan
Small all-terrain vehicle on a beach image by Sergey Sukhorukov from Fotolia.com
All Wheel Drive (or AWD) is a system in which all four wheels of a car work simultaneously to improve traction and handling. While it is possible for a car to have continuous AWD capabilities, it is much more common for one pair of wheels to activate only when sensors detect that the other pair has started to skid. AWD systems have advantages and disadvantages
In intermittent AWD systems, the rear wheels are activated when the sensors detect a skid of the front wheels. In these circumstances, the vehicle effectively detects and compensates for dangerous driving conditions, such as standing water, snow, ice, or gravel, which could otherwise compromise vehicle control. By engaging the second set of wheels, the vehicle experiences two additional contact points on the road surface, allowing a greater likelihood of its tires sticking to the surface and allowing the driver to maintain control. The added weight of the AWD systems also encourages more grip on the road, and the additional contact points distribute the vehicle’s weight more evenly over the propulsion points.
The main disadvantage of an AWD vehicle is its cost. The drivetrain and related equipment needed to provide both continuous and intermittent AWD is complex and expensive, often requiring sensors and computers that are not needed on two- or four-wheel drive vehicles. This cost increases the initial market value of the vehicle and can also affect the cost of repairs. In addition to these costs, AWD systems require more fuel to drive additional wheels and are less fuel efficient than comparable two-wheel drive vehicles.
Stopping distance and collision avoidance
While the weight of AWD vehicles improves their handling, it also increases the distance they need to stop. In a scenario where the vehicle must stop suddenly and cannot swerve or turn, a collision is more likely than with a lighter car. In similar circumstances, but where an accident can be avoided by turning, AWD vehicles offer superior collision avoidance than similar vehicles with less effective steering and turning capabilities.