Once exclusively the domain of trucks and SUVs, four-wheel drive (also known as 4WD or 4×4) and its modern sibling all-wheel drive (AWD), have spread across a number of models and makes in recent years – from small cars to crossovers and even luxury sedans. Besides the obvious – gaining traction with engaging four-wheels instead of two – there have been other reasons for this growing segment.
While there are many different variations between the two systems – from the traditional Jeep CJ to the Audi quattro models and even Subaru (which boasts three completely different AWD systems!), I plan to keep this simple. First a basic comparison between the 4WD and AWD systems.
The traditional 4WD system was the first – referring to vehicles that have a transfer case not a differential, between the front and rear axles, meaning that the front and rear drive shafts will be locked together when engaged. This provides maximum torque transfer to the axle with the most traction, but can cause binding in high traction turning situations. Its mechanical nature means simple and positive engagement when called for, but the system doesn’t have the ability to adjust for wheel specific issues like traction or contact with a different surface – i.e. one wheel in sand as opposed to the other three on pavement. They are also either full-time or part-time 4WD selectable. 4WD is not intended for high speeds without a limited-slip mechanism.
All wheel drive (AWD) or “permanent multiple-wheel drive” refers to a drive train system that includes a center differential between the front and rear drive shafts. This is normally coupled with some sort of anti-slip (traction control) technology that allows the differentials to spin at different speeds, but still maintain the ability to transfer torque from one wheel in case of loss of traction at that wheel. Typical AWD systems work well on all surfaces.
While the use and application of the traditional 4WD system is obvious – particularly in off-road and low traction situations, the application of AWD in passenger cars and crossovers is more varied.
- Performance – Increasing horsepower in recent years used to mean upper limitations of handling and performance for cars – especially front wheel drive (FWD) models. The application of AWD and same-length half-shafts for power to the front wheels means that more power can be effectively applied to all wheels in a smaller package. The result? More speed, power AND control at the same time.
- Handling – The inherent design of AWD systems means that power can be seamlessly transferred not just front to back, but side to side as conditions warrant. The result is smaller performance vehicles that handle like they are on rails.
Things to remember – typical 4WD or AWD system equipped vehicles carry a premium over regular FWD or RWD vehicles. For passenger cars it usually adds about $1,800 to the purchase price. The hardware also adds to maintenance costs over time. AWD equipped vehicles also include the complexity of the electronic controls used to operate the system.
Add to both types of systems heavy duty suspension system components, heavy duty transmission components and transmission cooling systems, wheels and tires and the operating costs add up quick.