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Besides the name, there's not an inherent difference. It really depends on what a particular mfr wants to call his system.
In general, a "four wheel drive" vehicle has a part-time 4wd system, which can (and should) be switched off for use on dry pavement. Generally these vehicles do not have a center differential (in the xfer case) or other means of allowing a speed difference between front and rear drive. In other words, in a 4wd vehicle w/ 4wd engaged, the front driveshaft is forced to spin at the same speed as the rear driveshaft. A tight turn on dry pavement will result in tire chirping and a "hopping" sensation, because the front and rear wheels are following different curves and would like to spin at different speeds.
In general, an "all wheel drive" vehicle has a full-time 4wd system, which cannot be manually disengaged. These vehicles will always have some means of allowing slip between the front and rear drive, to facilitate maneuvering on dry pavement. The AWD vehicle won't chirp or hop in a turn on dry pavement.
Why I say it's just a name (depends on mfr): A long time ago, I used to have a Jeep with "Quadratrac" 4WD, which fits my definition of AWD perfectly. The Quadratrac transfer case had a limited slip lockable differential built in, which allowed the vehicle to operate like an "AWD" on pavement, and like a "4WD" on slippery stuff.
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04-23-2002, 02:36 PM
4WD vs. AWD
