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North American Trucks
2016-03-25 09:18:15
In North America, the combination vehicles made up of a powered truck and one or more detachable trailers, are known as semi-tractor-trailers, tractor-trailers, semis, big rigs, semi trucks or eighteen-wheelers.
The tractors, or powered trucks, typically have two or three axles; those built for hauling heavy-duty commercial-construction machinery may have as many as four or five axles, some often being lift axles.
The most common tractor-cab layout has a forward engine, one steering axle, and two drive axles. The fifth-wheel trailer coupling on most tractor trucks is movable fore and aft, to allow adjustment in the weight distribution over its rear axle(s).
Ubiquitous in Europe, but less common in North America since the 1990s, is the cabover configuration, where the driver sits next to, or over the engine. With changes in the US to the maximum length of the combined vehicle, the cabover was mostly phased out of North American over-the-road or long-haul service by 2007. Cabovers were notorious for being difficult to service, as the cab could not be lifted on its hinges to a full 90-degree forward tilt, and this severely limited access to the front part of the engine.
Trucks average between 4 and 8 miles per US gallon (1.7 and 3.4 km/L), with fuel economy standards requiring more than 7 miles per US gallon (3.0 km/L) efficiency by 2014.
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