Tractor is simply said to be between the head and the car is traction tools (that is, the car head can be separated from the original car and traction of other cars, and the car can also be separated from the original head by the other car) the general large truck (semi trailer). Classification...
A tractor is a commercial vehicle equipped with a special device for pulling semi-trailers.
The front has the driving ability of the truck is called the tractor, the rear does not have the driving ability of the truck is called the trailer, the trailer is towed by the tractor.
There are two types of connection between the tractor and the trailer: the first is that the front half of the trailer is hung on the traction saddle above the rear part of the tractor, and the bridge behind the tractor bears part of the weight of the trailer, which is the semi-suspension; The second is that the front end of the trailer is connected to the rear end of the tractor. The tractor can only provide forward pulling force and drag the trailer away, but it cannot bear the downward weight of the trailer. This is the full trailer.