4WD vs AWD
What's the Difference?
What's the difference between four-wheel-drive and all-wheel-drive?
There is a perception that both terms actually mean the same thing. Yes, they do, but they represent two different ways of delivering traction to all four wheels when they need it.
The term Four-wheel drive comes from a system where there are two axles with a differential each, connected by driveshafts onto a transfer case. The transfer case is where power from the engine and transmission is sent to the axles to manage traction. In the old days, this was done manually. A second lever on the floor controlled the transfer case, switching it from two-wheel to four-wheel drive. However, before the transfer case was engaged, the front wheel hubs had to be unlocked by a knob. That knob controlled whether the extra drive axle can be used to increase traction.
Transfer cases normally came with two gears – High and Low. High is where most traction is used – on wet, snowy and dirt roads that are drivable. Low is engaged for more difficult situations – such as crawling over rocks or icy conditions on a hill. The low gear in a transfer case restricts power to the axles, as long as the driver maintains a very low and safe speed to get through difficult terrain or poor road condition.
These days, four-wheel drive systems have become effortless. Automatic locking hubs, automated transfer case switching, even condition-based terrain management systems eliminate a lot of the grunt work of the past. Four-wheel drive systems are commonly found on pickup trucks and traditional SUVs.
This leads to the all-wheel drive system. Though the principle is the same, the system is much more simplified and automated than traditional all-wheel drive systems. The major difference is the use of a “center differential” rather than a transfer case. The center differential acts in the same principle as one on a drive axle, without any control on range and speed, except from the engine and transmission. The system is completely controlled by a computer connected back to the throttle, engine, transmission and axle hubs to ensure proper torque transfer to the axles.
On some all-wheel drive systems, there are some controls that allow for locking the center differential for complete all-wheel traction. It just takes a switch on the dashboard to enable all-wheel drive lock. Cars, minivans and crossovers usually have all-wheel drive systems available.