An all-wheel drive vehicle is one with a powertrain capable of providing power to all its wheels, whether full-time or on-demand.
The Jeep Wrangler is a 4×4 four-wheel drive vehicle equipped with a low-range gearbox, which provides the driver with a selection between low range or high range gearing
Hayes WHDX 70-170 6×6 tractor
The 8×8 tractor unit of the HETS (heavy equipment transport system)
Differential (mechanical device)
A differential is a gear train with three drive shafts that has the property that the rotational speed of one shaft is the average of the speeds of the others. A common use of differentials is in motor vehicles, to allow the wheels at each end of a drive axle to rotate at different speeds while cornering. Other uses include clocks and analog computers.
Differentials can also provide a gear ratio between the input and output shafts. For example, many differentials in motor vehicles provide a gearing reduction by having fewer teeth on the pinion than the ring gear.
Differential unit for a rear-wheel drive car, built by ZF circa 2004
Differential gears (in yellow) in a punched tape reader, built by Tally circa 1962
Illustration of a ring-and-pinion differential for a rear-wheel drive vehicle
Schematic diagram of a ring-and pinion differential