The Difference Between All-Wheel and Four-Wheel Drive

When we’re choosing a new offroad vehicle, one of the choices we need to make is how the vehicle is powered. The two main choices for modern vehicles is either all-wheel or four-wheel drive. Use this simple guide to learn the differences between the two.

The History Of 4WD And AWD

Jacobus Spyker developed the first four-wheel drive mechanism for cars in 1902. Many designers like Ferdinand Porche dabbled in all-wheel drive a few years earlier but it was Spyker’s car that featured the first transfer case and independent drive shafts we know today. Spyker also created Spyker Cars, who recently built the very impressive Spyker C8 Preliator.

Four-Wheel Drive

Spyker’s car had a fixed 4WD, ensuring both front and rear axles were always driven by the engine. Some examples of four-wheel drive cars include Land Rovers and Land Cruisers. Each wheel earns 25% of available engine power. The driver has 4H (four high, default setting) and 4L (four medium, low gearing). In these cars, the 4WD feature cannot be converted to standard two-wheel drive unless one of the drive shafts is physically removed. The breakthrough came from the Four Wheel Drive Auto Co. in 1911, which modified their transfer case to allow selectable 4WD, meaning that the transfer case allowed four-wheel drive part-time with high and low gear ratios.

Part Time Four-Wheel Drive

Such four-wheel drive vehicles typically occur in trucks. Two-wheel drive is the default mode, and should always be chosen on tarred roads and rough, unyielding surfaces.  The driver must manually employ the 4WD mode or, if this is performed on a tarred lane, a phenomenon called axle wind-up inevitably takes place. Axle wind-up happens because most part-time 4WD vehicles have no central differential and the torque disparity between front and rear axles puts transmission and/or axle pressure.

One of two nasty things occur to wind-up axles; either the tires slip or the transmission breaks: the former is bad enough, but the latter can be disastrous, and would require to fix properly.

Super Select Four-Wheel Drive

Mitsubishi’s Pajero has been around for many years, but their super-select is one of the finest four-wheel drive models out there. The Pajero has 4WD part-time, but drivers mostly abandon the 4H engine, only shifting to 2H if they want to save petrol on short, dead-straight highways . Furthermore, when driving over rugged terrain such as desert sand over 30 km/h, 4Hlc four wheel drive in high-range gear with gear train will lock the differentials. Another transmission choice is 4Llc (four low-range wheel drive with locking differentials), but the vehicle must be stationary before choosing this mode and speeds must preferably be kept under 30 km/h.

All-Wheel Drive

Technically, the term all-wheel drive can refer to a vehicle driven on all wheels including six-wheel or eight-wheel drive vehicles. Generally, companies apply the term to road-going cars. The Subaru Outback has X-mode, a complex traction control feature that mimics a limited slip differential, but when off-roading nothing beats a lockable diff. All-wheel drive also uses technology such as viscous couplings, torque converters, and other dark arts to switch seamlessly from one axle doing all the work or both axles splitting the load. Many vehicles have a back-axle tendency, while others favour the front-axle.