What is the difference between a semi-trailer and a full trailer?

Feature	Semi-Trailer	Full Trailer
Axles/Wheels	Wheels only at the rear.	Has both front and rear axles (at least two axles total).
Front Support	Rests on the fifth wheel of the tractor.	Supported by its own front axle(s).
Weight on Towing Vehicle	Yes. A substantial portion (the “kingpin” load).	No. It carries its own entire weight.
Connection Point	Fifth Wheel Coupling (a large, flat, rotating plate).	Drawbar (Pintle Hook or Ringfeder).
Primary Towing Vehicle	Semi-Truck (Tractor Unit).	Truck with a hitch, or another trailer (via a dolly).
Maneuverability	High (articulates at the fifth wheel).	Lower (follows the towing vehicle’s path).
Dominant Use	Long-haul highway freight (the most common type).	Road trains, specialized heavy transport, yard operations.
When Unhitched	Front rests on landing legs.	Stands on its own wheels.

Key Feature: It has wheels only at the rear. The front of the trailer rests on a fifth wheel coupling mounted on the towing vehicle (the tractor or prime mover).
Weight Distribution: A significant portion of the trailer’s weight (often 20-25%) is borne by the tractor unit itself through the fifth wheel. This creates a balanced, articulated connection.
Towing Vehicle: Requires a powerful tractor unit (a “semi-truck” or “prime mover”) specifically designed with a fifth wheel.
Maneuverability: Highly maneuverable for its size due to the articulated pivot point at the fifth wheel. It can navigate tight corners well.
Stability: Very stable at high speeds and on highways, which is why it dominates long-haul freight.
Common Uses: The absolute standard for long-distance road freight. You see them everywhere carrying shipping containers, dry vans, flatbeds, tankers, and refrigerated goods.
Visual Clue: The trailer appears to be “leaning” on the front of the tractor. When disconnected, the front of the trailer rests on retractable landing legs.

Key Feature: It is a complete, self-contained unit with both front and rear axles. It carries its entire own weight on its own wheels.
Weight Distribution: 100% of its load is on its own axles. The towing vehicle only provides pulling power and directional control through a standard drawbar (hitch).
Towing Vehicle: Can be towed by a wider range of vehicles: a standard truck (with a hitch), a road tractor, or even another trailer (in a B-double or road train configuration).
Maneuverability: Less maneuverable than a semi-trailer, especially in reverse, as it follows the path of the towing vehicle more rigidly.
Stability: Can be less stable at very high speeds if not carefully loaded, which is why they are more common in specific applications.
Common Uses:
- Dolly Converter: A special type (a “dolly” or “converter dolly”) is used to convert a semi-trailer into a full trailer, enabling it to be hooked behind another semi-trailer to form a B-Double or Road Train.
- Specialized Transport: Heavy haulage, low-loaders, and certain types of machinery transport where the load needs to be evenly distributed across many axles.
- Logistics Yards: Used within ports and large facilities for moving containers short distances.
Visual Clue: It looks like a complete, independent wagon. When disconnected, it stands fully on its own wheels.