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Re: Lucid AWD vs. 4WD explanation?

A simple explanation with techno-primer...


As a car moves down the road in a straight line all wheels are moving at
the same speed.  As it takes a corner each tire actually has to move at a
different speed (since each tire actually travels a different distance -
insides less than outsides and back less than front).  This difference of
speed must be accounted for. especially if all four wheels are to be


AWD can be used under any conditions without concern for drivetrain damage
or drivability problems.  The difference in tire speed is allowed for
WITHIN the vehicle's drivetrain.

4WD requires that the vehicle be taken out of 4WD on dry pavement.  In this
case, the difference in tire speed is NOT allowed for within the drivetrain
so must be accomodated EXTERNALLY by actually allowing the tires to slip
(like when on ice, snow, or mud).


In 4WD there is no center differential to allow for front to back speed
differences, in AWD there is.  Most good AWD systems also allow for
transmitting power to the wheels that have the most traction (a regular
open differential actually sends most of the power to the wheel with the
LEAST traction!).  Two good systems (my own judgement) are the viscous
coupling and the Torsen (torque sensing) - both work fine and are reliable.

Does that help?


Mike Marion
Manager, Optronics TAC
(800) 344-8695 -or- (978) 250-5314