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Originally Posted by Chris
Marketing if a funny thing, and is mostly BS.
But there are supposed to be a few fundamental differences in TRADITIONAL 4WD and AWD.
4WD is a part time system, if it isnt part time, its not a 'real' 4WD system. It uses a transfer case, that, when engaged, splits the power by a certain, fixed ratio between the front and rear tires (usually 50-50) Well, from how I understand, it is just a locking differential, so, it makes the same amount of rotations of the driveshaft go to each axle. So, if the front wheels are on ice, and the back wheels are nearly locked, more actual power is being sent to the rear wheels, and both the front and back spin at the same rate. (ie, the rear wheels are exerting a force of 10000newtons, the fronts, only 50 newtons).
A 4WD system is usually left in 2WD, to avoid wear on the transfer case, and possible, minor handling issues.
AWD, on the other hand, is a full time system, with power to wheels changing all the time. The power goes to a transfer case (which will usually be an open or limited slip differential, or a fancy clutch or hydralic system), from there to the front and rear axles, which will have usually an open or limited slip differential, or something fancier.
This works better for things like casual rough weather driving, since its always on.
For real offroad situations, its not as good, there is too much slip in the system, wheels with traction wont get as much power. Still, a good AWD system can be adequate for most cottaging adventures, with tires playing a pretty big role.
Of course, the perfect off road system is totally unpractical for normal use; a locking diff, and locking front and rear ends. Try this for normal driving, fully locked, and you'll end up breaking things, besides handling being terrible.
(note, most factory 'locking' diffs arent lockers, they're limited slips)
So, if you do real offroading, a 4WD system is better, for everyday use, AWD is better, plus, it provides AWD when you might not be expecting to need it, and in a 4WD vehicle, you'd be in 2WD.
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