Four wheel drive is a term that is sometimes used interchangeably with all wheel drive and describes how a vehicle to transfers the engine power to all four wheels. However, there are distinct differences between these two different types of drivetrains.http://www.4x4abc.com/4WD101/definition_part.html Usually, either the front or rear wheels are driven by the engine's power. A four-wheel drive system offers a distinct advantage when traction is limited in slippery conditions such as on snow, mud, loose gravel or sand. http://www.2carpros.com/how_does_it_work/4wd.htm
Four Wheel Drive Vs. All Wheel Drive
Four Wheel Drive and Inclement Weather
Do-it-Yourself Four Wheel Drive Video
A humorous television show teaches viewers how to make their own four wheel drive vehicle by literally taping two vehicle halves together. Corners are cut and safety measures are skipped as two vehicles are merged into one using a large saw, duct tape and little else. It is pointed out that a stationary vehicle can also be created by joining the two back halves together, though it won't have the ability to steer.
References
Fast Facts
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Fact:
Some four wheel drive vehicles are viewed negatively by environmentalists
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Fact:
The superior grip of a four wheel drive vehicle may make pulling a trailer easier
