4WD generally has a transfer case with low and high range gearing for
off-road low-speed use.
AWD provides drive to all wheels but does not have the low range option.
If you do not have a center differential between the front and rear
driveshafts, operating on dry pavement can induce driveline windup since
the front wheels need to travel different distances than the rear wheels
due to turning and the Ackerman effect. On loose gravel, dirt or snow,
the tires will slip so this is not a problem.
Mike Myers
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