alt Hacker NewsThis distinction (although I know it) has never made logical sense to me.
I only have four wheels. If all the wheels are driving, and I only have four wheels, then...
Again, I do know what the conventional difference is. But it's just that: convention. Unless you memorized the convention beforehand, there's really no way to decipher why 4WD/AWD has any meaningful distinction, nor which of the two specific names maps to which mechanism.
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4wd - locking transfer case in the middle. Best for off road.
AWD - clutch packs. Best for nasty conditions on road, IMHO.
It's more of an industry wide thing:AWD means all wheel drive even when the vehicle has more than 4 wheels. So in the case of a vehicle with more than 4 wheels, 4 wheel drive would indicate four of the wheels are driven and the remainder are idlers. For instance 6x4 would indicate six wheels with four driven wheels.
https://en.wikipedia.org/wiki/Six-wheel_drive
So nwheels x n driven wheels.
4WD: Distribution of power to the wheels is static. AWD: Distribution is dynamic.
4WD vehicles are often part-time 4WD, meaning they can be switched between 4WD and RWD or FWD.
AWD vehicles are full-time AWD because part-time AWD is unnecessary given that the drivetrain delivers power where it's most needed.