Permanent 4x4 vs AWD

[Anupam Routh]

Greetings! Ford Explorer sells either with permanent 4x4 (which has low and high extra gear for real sticky situation) and AWD. Why any one will buy AWD When permanent 4x4 is available? I have AWD Ford five hundred and 4x2 ST. Only thing I can think is AWD is cheaper to make than 4x4 permanent.



According to dealer 4x4 permanent can be driven an ordinary pavement as a RWD SUV. When the SUV feels the need it gets traction on front wheels. (This just opposite my AWD Ford 500 - where the car drives like FWD and when needed applies traction to rear Wheel)



Please explain me the reasons? With thanks.

 

[Carey Frennier]

http://www.4x4abc.com/4WD101/diff4WD_AWD.html

 

[Chris Kulbaba]

Not to hijack the thread, but in the Fords that have the AWD, how do you know when its on or not? The STA has AWD, but it only comes on when required, how do you know when that is. The traction control light comes on when thats in use but I dont think there is any indicator about the AWD.

 

[TrainTrac]

Isn't it in AWD mode all the time by default? Or is it 2WD by default and goes into AWD mode on demand?



What does your owner's manual say about the AWD mode?

 

[Carey Frennier]

It's in AWD all the time. When the light flickers it's using the TC to move the energy around to get the best possible traction.

 

[Michael Cacioppo]

In my understanding of permanent 4X4 is that when in 4X4 equal power is put to the front differential and back differential. Its always 50/50. Since the sum of the revolutions of both the back set and front set of wheels MUST be the same, there is scuffing of tires when your vehicle transverses different arcs in a turn. That's why you should use 4x4 permanent (non differential transfer case) when on wet or snowy roads as dry pavement puts excessive stree on the drivetrain. AWD has a a differential type transfer case. In some models the rear wheels are driven unless slippage is noted and then power is applies to the other end of the vehicle in some proportion from 0/100%. Other vehicles drive the front wheels until slippage then transfers some power to the other end of the vehicles. Since the front and back differentials in an AWD system do not require a 50/50 distribution, the two sets of wheels are not required to rotate at the same velocity, thus no scuffing. In very limited traction situations the permanent 4x4 is better since power will always go to both front and back regardless of traction whereas AWD with keep switching looking for traction. That I believe is a general outline between the two types.

 

[Keith McElroy]

I had a 97 AWD Mountaineer and I could never tell if roads were icy until I applied the brake. It make it a little dangerous in the winter. Now, I drive in 2WD until it slips, then switch on the 4WD.