Eight-wheel drive (also known as 8WD or 8×8) is a powertrain system that enables all eight wheels of an eight-wheeled vehicle to be drive wheels (i.e., to receive power from the engine concurrently).
Unlike four-wheel drive drivetrains, the configuration is mostly limited to heavy-duty off-road and military vehicles, such as armored vehicles, tractor units, or all-terrain vehicles like the Argo Avenger.
Since it only has eight wheels, every one of them must be driven. Even though all twelve wheels are motorized and each rear axle has two pairs of ganged “dual” wheels, the classification “8×8” still applies. Rarely, for instance on the Sterling T26, can ganged “dual” wheels be installed on the two front axles.
Single wheels on each axle, often known as super singles, are the standard for the majority of military applications where traction/mobility are prioritized over cargo capacity. The rear two axles of some vehicles, typically recovery trucks or heavy tractor units, feature wider single tires than the front two axles.
Both in the military (as tank carriers and artillery tractors) and commercially (in logging and heavy equipment transporting both on- and off-road), heavy hauler and ballast tractor 8x8s have a long history of use as prime movers.
The majority of eight-wheel-drive trucks have two forward axles, two at the back, and only one steering pair. There are occasionally vehicles with a single front axle and three rear axles (tridem), such as the Oshkosh M1070 tank transporter. Such arrangements often have the front and back axles steering. Other configurations include the ZIL-135’s.
The axles (which often have independent suspension) on many wheeled armored vehicles with an 8×8 driveline are spaced more equally. The rearmost of modern 8×8 wheeled armored vehicles has steering.