A semi truck is a large vehicle that includes a towing engine, known as a tractor in north america as well as truck in lots of other places. It is also referred to as a transport in Canada; prime mover in Australia and usually a 18-wheeler vehicle in the United States.
A semi-trailer does not trail totally behind the towing car or truck, but is attached at a point that is just forward of the rear-most axle of the towing system. This is done so that a large portion of the weight of the trailer is carried by the prime mover. This arrangement means that both tractor and semi-trailer will have a remarkably distinct design than a rigid truck
The combination vehicles comprised of a powered truck and one or more detachable trailers, are known as "semi truck vehicles"made up of a powered truck and one or more detachable trailers, are known as "semi truck vehicles"
Trucks:
The tractors have two or three axles; those designed for hauling heavy-duty commercial-construction machinery may have as many as 4 or 5 axles, some often being lift axles.The most common tractor layout has a forward engine, one steering axle, and two drive axles.
Trailers:
The cargo trailer usually has a "tandem" axle pair at the rear, each of which has dual wheels, or eight wheels on the trailer, four per axle.[b] Many trailers are equipped with a movable tandem to allow adjusting the weight distribution. The combination of eight tires on the trailer and ten tires on the tractor is what led to the moniker "eighteen wheeler".
We can also connect 2 trailer to the tractor,of which to connect the second of a set of doubles to the first trailer, and to support the front half of the second trailer, a converter gear, also known as a con-gear or dolly is used. This apparatus has one or two axles, a fifth-wheel coupling for the rear trailer, and a tongue with a ring-hitch coupling for the forward trailer. These longer vehicles, known as "longer combination vehicles" or LCVs), and may allow them to operate on roads other than those that are part of the national network mostly.
