The Long And Short Of Semi-Truck Trailers
A semi trailer truck is an articulated vehicle that is combined of two moving parts, the engine, also called the tractor and the trailer that carries freighter. Unlike a rigid truck and trailer vehicle, some of the weight that is carried in the trailer rests on the rear axle of the towing unit or the tractor. Semi trailer trucks are used to move large units of cargo over long distances on the surface. The major difference between the semi trailer trucks and the other rigid trucks is that in the semi, the trailer does not trail completely behind the tractor but it is flexibly attached at a point on or before the rearmost axle of the towing unit.
There are certain characteristics that are only unique to the semi trailer which make them unique on the road. Note that while in the USA, there is strict weight limit to protect the roads, a big rig, as they are sometimes called, can carry much more weight than what it is allowed. It is a unique vehicle in that:
ï A semi tractor in the USA (normal sized one) has three axles and is in normal cases fitted with ten wheels. The front axle has two single wheels and it is used for steering. There are other two rear axles and each has a pair of wheels, called dualies or doubles.
ï The freight carrier or the cargo trailer has two tandem axles in the rear. Each of the two axles has four wheels or two doubles. This makes the cargo trailer wheel count eight wheels. This, in addition to the tractor’s ten wheels makes the total number of wheels 18. Thus, the semi trailer trucks are mostly referred to as 18-wheelers.
ï There are smaller tractor units in the USA that are used to tow smaller cargo trailers in the downtown where the big rigs would have trouble maneuvering. Such have one axle at the rear of the tractor and usually do not have a sleeper cabin.
ï The 18-wheelers have a sleeper cabin that is large enough for a burly driver to curl comfortably.
ï Semi trailer trucks are fitted with the fifth tandem axle of supporting wheels, which can be used to adjust the weight over the other axles.
Among the changes expected soon in the semi trailer trucks is the use of the super single tires instead of the doubles. Economists have proved that the single tires allow for more weight and that when used; this articulated vehicle can save up to 10% in fuel.
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