An all-wheel drive vehicle (AWD vehicle) is one with a powertrain capable of providing power to all its wheels, whether full-time or on-demand. The most common forms of all-wheel drive are: ;1x1 : All unicycles
Reflecting one axle with one wheel capable of being powered. ; 2x2 : Some motorcycles and bikes
Reflecting two axles with one wheel on each capable of being powered. ;

4×4 Four-wheel drive, also called 4×4 ("four by four") or 4WD, refers to a two-axled vehicle drivetrain capable of providing torque to all of its wheels simultaneously. It may be full-time or on-demand, and is typically linked via a transfer case ...

(also, four-wheel drive and 4WD): Reflecting two axles with both wheels on each capable of being powered. ;

6×6 Six-wheel drive (6WD or 6×6) is an all-wheel drive drivetrain configuration of three axles with at least two wheels on each axle capable of being driven simultaneously by the vehicle's engine. Unlike four-wheel drive drivetrains, the configurat ...

(also, six-wheel drive and 6WD): Reflecting three axles with both wheels on each capable of being powered. ; 8×8 (also, eight-wheel drive and 8WD): Reflecting four axles with both wheels on each capable of being powered. Vehicles may be either part-time all-wheel drive or full-time: ;On-demand (also, part-time): One axle is permanently connected to the drive, the other is being connected as needed ;Full-time (also, permanent): All axles are permanently connected, with or without a differential. ;Independent : The wheels are driven, but not dependent on a central mechanical power coupling.

Usage of the terminology

Particularly in North America for several decades, the designation ''AWD'' has been used and marketed - distinctly from "4X4" and "4WD" - to apply to vehicles with drive train systems that have permanent drive, a differential between the front and rear drive shafts, and active management of torque transfer, especially following the advent of ABS. However, the designations ''AWD'' and ''all-wheel drive'' long predated the trend, with

Associated Equipment Company Associated Equipment Company (AEC) was a British vehicle manufacturer that built buses, motorcoaches and trucks from 1912 until 1979. The name Associated Equipment Company was hardly ever used; instead it traded under the AEC and ACLO brands. ...

(AEC) producing AWD trucks in 1929 in conjunction with the British subsidiary of the pioneering American firm,

Four Wheel Drive Auto Company Four-wheel drive, also called 4×4 ("four by four") or 4WD, refers to a two-axled vehicle drivetrain capable of providing torque to all of its wheels simultaneously. It may be full-time or on-demand, and is typically linked via a transfer ca ...

. Additionally, General Motors began manufacturing a line as "all-wheel drive" as early as the late 1930s. This distinction in terminology is not generally used outside North America.

Characteristics

When tire grip is good during road driving, a differential is used between the axles to avoid driveline windup. This is not required off-road, as the limited grip allows the tires to slip. All-wheel drive vehicles designed for extensive off-road use may not have such a differential, and so they suffer from wind-up when used on-road. Selectable 4WD also avoids this problem and requires only a simple dog clutch in the transfer case, rather than a differential. For this reason, most early off-road vehicles used that system; e.g., Jeep,

Land Rover Land Rover is a British brand of predominantly four-wheel drive, off-road capable vehicles, owned by multinational car manufacturer Jaguar Land Rover (JLR), since 2008 a subsidiary of India's Tata Motors. JLR currently builds Land Rove ...

. As vehicles became more sophisticated and tires gave better winter performance in the 1960s there was an interest in giving the benefits of all-wheel drive to conventional cars; not for off-road use but for winter use in snow or on wet roads. Exotic vehicles such as the high-powered Jensen FF followed by the AMC Eagle,

Subaru Leone The Subaru Leone is a compact car produced by the Japanese automaker, car manufacturer Subaru from 1971 to 1994. The word ''leone'' is Italian for lion. It was released as a replacement for the Subaru 1000 and was the predecessor of the Subaru Im ...

and Audi Quattro series were the first to offer all-wheel drive in a high-speed road-based car. These, particularly the Quattro, would extensively develop this drivetrain with the use of viscous couplings and differentials to provide a safe and drivable car. The first off-road / on-road hybrids such as the Range Rover also chose the permanent all wheel drive system rather than manual selection. Selectable 4WD has both axles rigidly coupled together, which has some advantages in very poor off-road conditions. To gain the same advantage in a permanent AWD system with a differential, the differential can be locked manually with a differential lock. As this control is frequently misunderstood and mis-used, which can then cause damage due to wind-up, they have tended to be replaced by automatic locking through the viscous couplers.

References

{{DEFAULTSORT:All-Wheel Drive Off-road vehicles Car layouts Drivetrain

Usage of the terminology

Characteristics

See also

References