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.

Four-Wheel-Drive

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.

All-Wheel-Drive

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.

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