Tractor units on the market are primarily categorized into two types: semi-trailer tractors and full-trailer tractors.
1. Semi-trailer tractor: The front section of the trailer rests on the fifth-wheel coupling located at the rear of the tractor unit, meaning the tractor's rear axle bears a portion of the trailer's weight.
2. Full-trailer tractor: The front end of the trailer is connected to the rear of the tractor unit; the tractor provides only forward pulling force to tow the trailer but does not bear any of the trailer's downward weight.
