Four-wheel drive systems - there are a number of 4WD systems, generally split between full-time and part-time operation.

As the names imply, power is sent to all four wheels either all the time or some of the time.

Full-time 4WDs can be driven on all road surfaces.

Some full-time systems are "selectable", running in two-wheel drive when the driver so chooses.

Part-time systems run as two-wheel drive until the driver selects four-wheel drive for off-road use.

On-demand part-time systems automatically transfer power to the rear wheels on all surfaces when slip is detected.