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What Is All-Wheel Drive?


AMG all-wheel drive system for compact cars

Vehicle marketing and reviews make frequent mention of all-wheel drive and describe improved capabilities in challenging conditions.  But wait—isn’t that the same as four-wheel drive?  It is, yet it isn’t.  Here’s a brief rundown to provide a little clarity.

Different than four-wheel drive.  Without getting bogged down in technical semantics, let’s think of four-wheel drive (aka 4WD or 4x4) as the typically more mechanical system found in pickups and tougher SUVs.  These vehicles might have a lever on the floor or center console to engage drive modes, usually including two-wheel drive as well as a four-wheel drive low or “4L” range.

Always on.  Whether a family minivan, crossover, luxury sedan or million-dollar exotic, all-wheel-drive vehicles always have torque going to each corner, but that will rarely be an even 25 percent per wheel.  Distribution is continuously dynamic, determined by vehicle setup and driving conditions.  In some performance cars, the driver can dial in a front/rear torque split or select driving modes. (In a few cases, these systems can decouple an axle for better fuel economy...at which point the dividing line becomes very grey.)

Seamless.  Aside from those exceptions, all-wheel drive works seamlessly as you go.  There is no remembering to activate it when conditions get dicey or need to turn it off on dry pavement.  Faster than humanly possible, the computerized system manages power division between the wheels as they grip and slip.  All-wheel systems are not foolproof by any means but generally deliver better control and traction than counterparts with only front- or rear-wheel drive.

More aiding than enabling.  So with this in mind, is all-wheel drive superior to four-wheel drive?  That depends on conditions, expectations and needs.  All-wheel-drive vehicles tend to have less ground clearance and more tender tires.  Soft-roading might be fine for some of these, but serious off-roading is out. 

Four-wheel-drive’s more mechanical setup handles higher torque loads better, and can be controlled more directly by the driver in extreme conditions when human input is preferred over computer control.  All-wheel drive excels as an aid when road traction is at a premium, without the driver doing anything beyond careful execution as normal.

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