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Semi Trailers and all about it …

A road tractor coupled to a semi-trailer is often called a ‘semi-trailer truck’ or simply ‘semi’ or ‘an articulated lorry’. When going to purchase a semi trailer to be used as cargo trailer form a trailer shop, it is very important to understand a few important points about it. A semi-trailer is a type of trailer without a front axle (axle is a central shaft for a rotating wheel or gear). It only has the rear wheel and frame assembly, a large proportion of its weight is supported by a detachable unit called as a ‘dolly’.
The dolly here is equipped with a fifth wheel to which the semi-trailer is coupled. It is a kind of small trailer (2 wheels and a frame assembly) usually attached to a semi-trailer so as to support it. Though used as an integrated part of the trailer-towing vehicle assembly a dolly might need its own rear lights and a registration plate.
When more than one trailer is used then a semi trailer may also be attached by the tail of another trailer. So as to support semi trailers when not coupled, they are equipped with the legs which can be lowered called ‘landing gear’.