Four-wheel drive, 4WD, or 4x4 ("four by four") is a four-wheeled vehicle with a drivetrain that allows all four wheels to receive torque from the engine simultaneously.
In the United States, these cars are often, but not always, included in the broader sport utility vehicle category. While many people associate the term with off-road vehicles, powering all four wheels provides better control in normal road cars on many surfaces, and is an important part of rally racing. In some mechanic circles the term "4 by 4" also denotes the number of drive wheels and the number of speeds the car has, so the term "5 by 4" would denote an automobile with 5 speeds and 4 drive wheels.
The term four-wheel drive describes truck-like vehicles that require the driver to manually switch between two-wheel drive mode for streets and four-wheel drive mode for low traction conditions such as ice, mud, snow, slippery surfaces, or loose gravel.
All-wheel drive (AWD) is often used to describe a "full time" 4WD that may be used on dry pavement without destroying the drivetrain (It should be noted that "Full-Time" 4WD can be disengaged and the center differential can be locked, essentially turning it into regular 4WD. On the other hand, AWD cannot be disengaged and the center differential cannot be locked.
The early tractors were converted to 4-wd by 3rd party converters as manufacturers did not see the market as worthwhile at first, now they nearly all offer 4-wd versions as standard.
Extract from Wikipedia article; http://en.wikipedia.org/wiki/Four-wheel_drive see here for full article]
|This page uses some content from Wikipedia. The original article was at Four-wheel drive. The list of authors can be seen in the page history. As with Tractor & Construction Plant Wiki, the text of Wikipedia is available under the Creative Commons by Attribution License and/or GNU Free Documentation License. Please check page history for when the original article was copied to Wikia|