All-wheel drive is great to have for winter in the snow belt or mountains, as well as for peace of mind in other traction-challenged driving conditions. It’s not a free ride, as buying and driving an AWD vehicle can entail significant cost premiums.
Most AWD systems offered today are designed to help in bad weather or for some weekend soft-roading, not for serious off-road use.
They drive just the front or rear wheels most of the time but automatically send power to the other axle when the electronics sense wheels slipping; more sophisticated systems can vary torque distribution side to side or even to individual wheels to enhance performance. While all AWD systems are electronically controlled, they increasingly vary mechanically.
More traditional AWD systems distribute power via a transfer case, drive shaft and multiple differentials. Some hybrids (particularly from Toyota) have no mechanical connection and instead add an electric motor for the rear axle, and some electric vehicles use two, three or even four electric motors to drive both axles or individual wheels. Meanwhile, more robust 4WD systems add capability for true off-roading; they are found mostly on pickup trucks and other vehicles designed for such use. The mechanical distinctions between AWD and 4WD have been muddied in recent years by electronics, but they still differ in capability and driver control.
