A semi-trailer together with a tractor unit makes up an articulated truck (also called an articulated lorry). Semi-trailers can be purchased with various substructures or body types, just like trucks. Since semi-trailers are so much cheaper to purchase than trucks, they are also more flexible to operate. Different criteria are important when buying a semi-trailer than with a motorised vehicle.
In general it is important to check the axles, undercarriage, brakes and electrics. Also important to check is the condition of the tyres, which can offer valuable clues to the frequency of use and any possible defects. The semi-trailer substructure should also be inspected. Box and Tanker semi-trailers should be checked for water tightness, while refrigerator units in Reefer/Isolated/Freeze semi-trailers should be examined to ensure they are working correctly and have been regularly maintained. Lowbed semi-trailers should be inspected for physical damage in the trailer structure. Finally, it is important to ask what the semi-trailer was used for in the past as this also can affect the general condition of the semi-trailer.