...

Axle configuration

A tractor unit can have many axles depending on axle load legislation. The most common varieties are those of 4x2, 6x2 and 6x4 types, where a 6x4 has three axles, with two of the axles driven. 6x4 units are more common in long distance haulage in larger countries such as the USA and Australia. In Europe, the 4x2 and 6x2 variants are more commonplace. Those with three axles or more can have more than one steering axle, which can be also driven. Most 6x2 units allow the undriven rear axle to be raised when lightly loaded, or running without a trailer, to save tyre wear, and increase traction. The axle configurations are usually based upon axle load legislation, and maximum gross vehicle weight ratings (GVW). Heavier versions of tractor units, such as those used in heavy haulage and road trains, tend to have four or more axles, with more than one axle driven. In certain countries (such as Switzerland), a certain amount of weight must be spread over driven axles, which lead to heavier varieties having six-wheel drive, otherwise another tractor unit would have to be used. The heavy haulage variants of tractor-units are often turned into a ballast tractor by fitting temporary ballast, because their chassis allows a high GVW which may go beyond the legal limit, hence requiring special permits. Read full entry

This entry is from Wikipedia,the leading user-contributed encyclopedia.It may not have been reviewed by professional editors(See full disclaimer)