In road transportation, semi-trailer and full trailer are two common types of freight vehicles, but many people easily confuse them. The core difference between the two lies in the connection method and load-bearing structure with the tractor: the semi-trailer only has wheels on the rear half, and the front end is connected to the saddle of the tractor through a traction pin, with some weight carried by the tractor; A full trailer has a complete frame and independent wheels, connected to the tractor through hooks, and all weight is borne by itself. In the first quarter of 2025, semi trailers accounted for 68% of the domestic road freight volume, while full trailers only accounted for 12%. This gap is closely related to the transportation efficiency and flexibility of both. This article combines the latest transportation cases in 2025 to analyze the differences between semi-trailer and full trailer from multiple dimensions such as structure, driving, and regulations, helping you quickly distinguish between these two types of vehicles and understand their application advantages in different scenarios.
1、 Structural differences: The connection method determines the essential difference
（1） Semi trailer: a "semi independent three-dimensional" vehicle that relies on the towing vehicle to carry the load
The frame of the semi-trailer is in an "L" shape, with no wheels at the front end. It is connected to the saddle of the tractor through a thick traction pin (usually 50mm or 90mm in diameter) to form a stable support point. This means that the front weight of the semi-trailer (about 30% -50%) will be transmitted to the tractor, forming a unified load-bearing structure.
Taking the common 40 foot container semi-trailer as an example, its body length is about 13.7 meters, with only 2 sets (4-6) of wheels at the rear, connected to the frame through air suspension or steel plate springs. The traction pin seat at the front end of the frame is the core component that needs to withstand several tons of vertical pressure and horizontal tension. Therefore, it is forged from high-strength alloy steel with a tensile strength of over 800MPa.
The cargo compartment and frame of a semi-trailer are designed to be integrated and cannot be parked independently of the tractor. It must be supported by legs (lowered when parked) to support the weight at the front end. The legs of the new semi-trailer in 2025 are mostly electrically controlled, reducing the folding time from manual 3 minutes to 30 seconds and improving loading and unloading efficiency.
（2） Full trailer: a completely independent "overall structure"
A full trailer has a complete frame and an independent walking system, with wheels (usually 2-3 axles) at the front and rear, connected to the trailer's tail by a tow bar (or towing frame). All its weight (including goods) is borne by its own wheels, and the tractor only provides traction and does not bear vertical loads.
A typical full trailer, such as a 10 meter box type full trailer, has a straight through frame structure with a towing ring at the front end connected to the towing vehicle hook, and an independent braking system and lighting device at the rear end. Due to the lack of dependence on the towing vehicle, the full trailer can be parked separately from the towing vehicle, and even the parking angle can be adjusted by its own legs.
The towing rod of the full trailer is equipped with a buffer spring at the connection with the frame, which can reduce the impact force during starting and braking. By 2025, some full trailers will be upgraded to hydraulic buffer traction devices, reducing the impact acceleration from the traditional 5g to 2g, effectively protecting fragile goods.
