4WD vs. AWD: What’s the difference?


Since the explosion of the SUV market in the mid-1990s, many different companies have touted various forms of vehicles designed to take the driver where they please, rocks and mud be damned.  Four-wheel-drive, once considered to be a tool of the huntsman and rock-crawler, has now become a tool of the masses.  However, not all systems are created equal, and much has changed over the years, especially as car-based SUVs have increased in popularity.  Here’s a rundown of what some of the main differences are:

There are four basic types of drivetrains that fit into this category:

-Part-Time Four Wheel Drive (also known as ‘shift on the fly’): No center differential.  Four-wheel drive cannot be engaged on dry pavement because unwanted (and expensive) wear on the drivetrain will result.  This system is still popular in off-roading due to simplicity of design.  (Example: Jeep Wrangler, Toyota Tacoma)

-Full-Time Four Wheel Drive: Uses a center differential to compensate for tire speeds, can be left engaged on dry pavement.  (Example: Jeep Grand Cherokee with Quadra-Drive)  Some, however, may not have low-range in the transfer case.  This is the most common selectable system today.

-All Wheel Drive: All four wheels receive power at all times.  Normally will not have a transfer case, usually designed for on-road driving.  (Example: Mercedes 4Matic).

-“Active” All Wheel Drive: A newer development, where only one set of wheels may be receiving power until slippage at a non-powered wheel is detected.  At this point, power is sent to that wheel to maintain grip and direction.  (Example: Most Subaru products).

Each system has a distinct flavor to it, as well as varying degrees of capability and sophistication.

That said, there are still many other systems, but those four mentioned above are the most common families.


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