When referring to heavy vehicles, the term is increasingly applied to mean 'permanent multiple-wheel drive' on 2×2, 4×4, 6×6, or 8×8 drive-train systems that include a differential between the front and rear drive shafts.

Today in North America, the term is applied to both heavy vehicles and light passenger vehicles. Īll-wheel drive (AWD) historically was synonymous with 'four-wheel drive' on four-wheeled vehicles, and six-wheel drive on 6×6s, and so on, being used in that fashion at least as early as the 1920s. military would typically use spaces and a capital 'X' – as '4 X 2' or '6 X 4'. If this vehicle were a truck with dual rear wheels on two rear axles, so actually having ten wheels, its configuration would still be formulated as 6x4. Similarly, a 6×4 vehicle has three axles, two of which provide torque to two axle ends each. Accordingly, 4×2 means a four-wheel vehicle that transmits engine torque to only two axle ends: the front two in front-wheel drive or the rear two in rear-wheel drive. Syntactically, the first figure indicates the total number of wheels (or more precisely: axle ends) and the second indicates the number of axle ends that are powered. 'Four-by-four' or '4×4' is frequently used to refer to a class of vehicles in general.

SAE International's standard J1952 recommends only the term 'all-wheel drive' with additional subclassifications that cover all types of AWD/4WD/4x4 systems found on production vehicles.

The terms used by various manufacturers often reflect marketing rather than engineering considerations or significant technical differences between systems.

There is no universally accepted set of terminology that describes the various architectures and functions.

7.1 Center differential with mechanical lockįour-wheel drive systems were developed in many different markets and used in many different vehicle platforms.

3.4 World War II – a leap in AWD proliferation.

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