All-wheel drive (AWD) is a hot-ticket item in today's auto market, and is offered as an option on many cars. The system also commands a healthy premium over other drives, and for good reason.
The first production-car AWD systems were offered by German automaker Jensen in 1966, followed by Subaru, American Motors and Jeep in 1973.
AWD systems are intended to give a car the all-terrain flexibility of four wheel drive(4WD), the directional stability of front wheel drive(FWD), and the precision control of rear wheel drive (RWD).
An AWd system can start out as either FWD or RWD, but in either case uses a center differential similar to those found in the axles to allow the front and rear wheels to turn at different speeds.
Whereas FWD cars tend to plow on in whatever direction they're already going (understeer), and RWD cars tend to spin when turned hard (oversteer), a properly designed AWD system will always send the vehicle in whatever direction the steering wheel is pointed.
Some performance AWD cars like the Subaru WRX are designed to act like RWD car until the rear tires begin to slip, but most default to a FWD mode.
