Interesting...

4WD and AWD systems explained



4WD has been invented a very long time ago and various concepts have been tried. Here is a simplified synopsis of what is what. They are all 4WD, but have been given different names. Links within this page provide detailed insight.

Part time 4WD is a system that can only be used part of the time in four wheel drive.
This 4WD system was created to provide a vehicle with more traction to either carry higher loads and/or to travel in adverse terrain conditions. Clearly purpose built to do hard work. It can only be used for adverse terrain conditions - not for dry pavement.
Typical lever settings are 2WD, 4WD Hi, 4WD Lo.
Very good off-road. Most competent when combined with axle differential locks.
• 2WD setting must be used on dry pavement.
• If 4WD is selected, all 4 wheels are permanently powered.
Prominent example: 1942 Willys, Jeep Wrangler.


Full time 4WD can be used full time on all surfaces including pavement.
Full time 4WD was created to provide a vehicle with more traction and to make 4WD more useful for everyday life. It is also called permanent 4WD. The additional feature of a differential incorporated into the transfer case makes it possible to use 4WD all the time.
2WD is no longer available. Can still be a strong workhorse. Some rough terrain competence is retained - the priority is added stability as a safety gain for everyday driving.
Typical lever or switch settings are 4WD Hi, 4WD Lo. Very good off-road when center diff is lockable. Even better when combined with axle differential locks.
• All 4 wheels are permanently powered.
Prominent example: pre 2006 Mercedes M-Class,


Full time symmetric AWD is similar to full time 4WD - only it lacks the slow speed torque enhancing low range feature. Can be used full time on all surfaces including pavement.
Symmetric AWD was created as a safety feature for modern day vehicles. Not designed for hard work. Clearly a safer, more comfortable vehicle. Rough terrain competence has almost vanished - focus is on added stability and performance.
Limited use for off-road.
• All 4 wheels are permanently powered.
Prominent examples: 2006 Mercedes M-Class, Audi Quattro, most Subaru, before 2006 RAV4


Automatic asymmetric AWD was created solely as a stability enhancing system. Auto AWD can be used full time on all surfaces including pavement. AWD only briefly activates automatically when stability threatening conditions arise. Essentially a 2WD car with 2WD handling characteristics. Absolutely no adverse terrain capabilities. Clearly built for added road stability and safety.
Not recommended for off-road beyond graded dirt roads.
• 2 wheels are powered most of the time
• 4 wheels are only temporarily powered.
Prominent example: Volvo AWD, 2006 RAV4

A more detailed explanation of the differences between 4WD and AWD.

Many vehicles are offered with a combination of the systems outlined.

There is no commonly accepted standard - companies and especially their PR departments use terms for 4WD systems very loosely - tranparent consumer information is not their priority.

From what I've heard, there's not much of an effective difference between AWD and 4WD for on-road drivers. I'm not a professional on the matter, but as I understand it, the advantages of 4WD are moot except for off-road driving.