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4WD and AWD systems explained

A word of caution first. Manufacturers tend to obscure the true nature of their 4WD/AWD systems behind phantasy names like "Active 4WD", "Quadra-Drive", etc. - others might call their automatic AWD "Real Time 4WD".

There is plenty of confusion about what is what. Does it matter? Can't you just call "four wheel drive" "all wheel drive"? Yes you could. If all eight wheels of your big truck are driven, isn't it all wheel drive? Yes it is.
However, there are so many different 4WD systems on the market now that it is important to be precise and specific. It is important to call AWD when it is AWD and full time 4WD when it is full time 4WD. Just to say 4x4 is not sufficient any longer.
Wrong terms lead to misinformation - intentional or not. Wrong terms might make you buy something you neither want nor need! Do your homework before buying a 4WD - to get what you really need. If necessary, ask me.

There is no sanctioning body who ever established the definition of terms regarding 4x4. The terms I use below are the ones used internationally by engineers and competent magazines.
4WD has been invented a very long time ago and various concepts have been tried. Here is a simplified synopsis of what is what. Links within this page provide detailed insight.

#1 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 (4WD Lo is missing on some newer cars like Dodge Nitro).
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 examples: 1942 Willys, Jeep Wrangler, Toyota Tundra, etc etc.


#2 Full time 4WD - also called permanent 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. 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 examples: pre 2006 Mercedes M-Class, Mercedes G500, LandRover, RangeRover, Toyota Prado, Lexus GX470.


#3 Full time 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 dry pavement.
AWD was created as a safety feature for modern day vehicles. Not designed for hard work or off-road use. Rough terrain competence has almost vanished - focus is on added on-road stability and performance.
Limited use for off-road.
• All 4 wheels are permanently powered.
Prominent examples: 2006 and later Mercedes M-Class, Audi Quattro, most Subaru, pre 2006 RAV4


#4 Automatic 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 examples: Volvo AWD, 2006 and later RAV4, Honda CRV, Acura, Lexus.

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

So, is "real time 4WD" really 4WD? No, it is a sophisticated 2WD car with automatic asymmetric AWD. There is no commonly accepted standard how to name the different 4WD systems - companies and especially their PR departments use terms for 4WD systems very loosely - transparent consumer information is not their priority.

Many vehicles are offered with a combination of 4WD systems outlined above. Very confusing for consumers.

Here is more about why part time 4WD should not be used on pavement
 









ABS Confusion: ABS, traction control and stability control are three completely different things. ABS can not control traction or stability!
Traction control and stability control are based on the same hardware that is already in place for ABS. Both make use of the wheel speed sensors and a governing computer to procee wheel speed - however, traction control and stability control have sophisticated additional hardware (brake fluid pump, pressure reservoir, Gyroscope, lateral force sensor, steering angle sensor, etc) and a vastly more complicated software than ABS.





A variety of traction control systems are used in combination with many 4WD/AWD systems. These traction management systems (like ETS), are supposed to keep wheels from spinning after they slip - this job has nothing to do with 4WD/AWD per se, it is an additional stability feature (could be added to 2WD as well). The main job of traction management is to maintain equal wheel and axle speeds to keep you moving without wheel slip and losing control (like slipping sideways).


Vehicle stability programs, like ESP/ESC, are different from traction control. They assure directional stability under adverse driving conditions or driver errors. Their job is to keep you moving into the direction you intended to go. The biggest safety advance since ABS! A must have in a modern vehicle. It almost completely prevents roll overs.