- Full-time 4WD (or permanent 4WD) means the vehicle is constantly providing power to all four wheels, usually with power being shifted between the front and rear axles as needed. This provides maximum traction in both dry and slippery driving conditions and requires no action from the driver to activate it.
IMPORTANT: Full-time 4WD doesn't provide as much mobility off-road as part-time 4WD does, because the system is designed such that it allows a set of wheels (front or rear) to spin if they don't have traction.
- Part-time 4WD refers to a vehicle with selectable 4x4 or 4x2, requiring the driver to manually shift between 2WD and 4WD using either a lever or a switch. With part-time 4WD, you can "shift on the fly" (switch between 2WD and 4WD while driving). Part-time 4WD gives you better traction on slippery surfaces because the front and rear sets of wheels are locked together. Thus, this is the optimum choice for most off-road conditions.
IMPORTANT: Vehicles with part-time 4WD systems should not be driven on dry, smooth road surfaces when in 4WD mode, or you will soon be spending a lot of money on repairs.
- Automatic 4WD is a full-time system that lets the vehicle operate in 2WD (either front or rear) until the system judges that 4WD or AWD is needed. It then automatically routes power to all four wheels, varying the ratio between front and rear axles as necessary. Usually a slipping wheel activates the system, however, some of the more sophisticated systems use software that switches the system to 4WD or AWD during specific driving conditions -- BEFORE a wheel begins to slip.
IMPORTANT: Automatic 4WD vehicles are not recommended for serious off-road driving because all four wheels are powered at all times, which is not wise under certain off-road conditions.