6×4

It is the most common form of drivetrain of semi-tractors[2] and heavy haul fixed-chassis cargo trucks in larger countries such as the United States and Australia; in Europe, 4×2 and 6×2 variants are more commonplace.

Between the wars there was a great interest in the development of vehicles with better off-road performance, both for the military and for the growing oil exploration industry.

A few aberrations of 6×6, 8×8 and even half-tracks were produced,[4] but these were mostly as gun tractors or recovery vehicles and were too complex and expensive for General Service trucks.

A standard lorry chassis with live axles suspended by semi-elliptic leaf springs was inadequate for military use.

[i][7] One of the best-known heavy tractor units of World War II, the Scammell Pioneer, used this bogie system.

However some mass-produced 4×4[ii] vehicles have had their load-carrying capability increased by adding an additional, unpowered, rear axle.