All Wheel Drive versus 4 Wheel Drive/4x4
Life used to be so simple. Pickups looked like
pickups. SUVs looked like SUVs. Everything else was a car. Today, there are so many fractured segments, subsegments, different
styles, and looks that some people might consider a certain vehicle a car,
while others call it a four-wheel drive, and still others think it's a
crossover.
Part-time 4WD
In newer models, the driver can shift from 2WD to 4WD High while driving, but
must come to a complete stop to shift into the 4WD Low setting. One drawback of part-time 4WD
is that it must be continually engaged and then disengaged in conditions of
light rain or snow. This type of system is best for people who really don't
need 4WD, but occasionally go off-roading and want a little extra security when
it snows.
Full-time 4WD
Unlike part-time 4WD, full-time 4WD is just that--a system that can continually
remain operating. As with part-time 4WD, the shift from High to Low must be made during
a complete stop on most vehicles. Full-time 4WD is best for people who
regularly drive in slippery conditions where constant shifting between 2WD and 4WD
can become tedious.
All-Wheel Drive
All-wheel drive is similar to full-time 4WD in that the system is always
sending power to the wheels, but AWD has no 2WD switch. It is always operating
in 4WD mode. When the road gets slippery, the AWD system locks the axles and
automatically distributes power to all four of the wheels. In many cases, AWD
vehicles have no on/off switch. If the AWD system
allows the driver to switch to a "low" range gearing setting, like in
the Dodge Durango and Toyota 4Runner, then it is probably intended for severe
off-road use. AWD systems work well in cars and crossover vehicles because they
don't add much weight and make them true all-weather vehicles.
One of the best systems is Subaru's Symmetrical AWD system. The setup starts with a well-balanced chassis and platform, keeping all the powertrain parts flat and relatively low to the ground. The front axle shafts are driven directly off the transmission, while the rear driveshaft is separately driven from the transmission through a center differential.
