Overall Industry Overview
Trailer parts encompass the core components used in the manufacturing, maintenance, and modification of semi-trailers and full trailers, serving a wide range of sectors including long-haul logistics, bulk cargo transport, construction logistics, and cross-border trade. Mature industrial clusters have emerged in regions such as Liangshan (Shandong) and Xuzhou (Jiangsu); notably, Liangshan serves as the nation's primary hub for trailer and parts production and sales, offering over a thousand distinct product categories. The market is segmented into three main sectors: OEM parts for new vehicle assembly, aftermarket replacement parts, and lightweight modification components. Functionally, these parts are classified into five categories: load-bearing structural components, running gear and braking systems, connection and support components, superstructure accessories, and electrical and safety components. The quality of these parts directly determines a vehicle's load capacity, operational safety, service life, and fuel efficiency, making them essential components for the export of trailers in international trade.
Trailer frame assembly
The chassis serves as the load-bearing foundation-or "skeleton"-of the trailer. It is primarily assembled by welding together two high-strength longitudinal beams (main girders), transverse cross-members, W-shaped support cross-members, and side beams; the material of choice is 16Mn high-strength alloy steel designed for automotive applications. Heavy-duty models typically utilize thickened I-beam longitudinal girders, whereas lightweight trailers designed for standard loads employ formed high-strength steel profiles. The cross-members feature a W-beam structure to distribute the vehicle's load and prevent the main girders from twisting or deforming under heavy loads. The front of the chassis houses the welded mounting bracket for the kingpin, while the underside secures the suspension and axle mounting points; the upper section supports the weight of the cargo body and the load itself. As the fundamental component subjected to the greatest stress, the chassis requires routine maintenance inspections focusing on issues such as weld cracking and the bending or deformation of the main girders.
Towing pin
As the sole load-bearing connection between the tractor and the semi-trailer, the fifth-wheel pin is a critical safety component. It comes in two mainstream specifications: the "50#" type, suitable for standard-load transport with a gross weight of up to 50 tons, and the "90#" type, designed for heavy-duty applications such as coal hauling and oversized cargo transport. Installation options include welded and bolted versions; the bolted type allows for individual replacement of the pin after wear, facilitating easier maintenance. Manufactured from forged 18CrMnTi alloy steel and subjected to carburizing and quenching, the pin features a wear-resistant, high-compression surface and a tough, impact-resistant core. Every unit undergoes mandatory non-destructive testing before leaving the factory to eliminate the risk of hidden cracks. Since the pin bears all traction and impact forces during starting, braking, and turning, it must be replaced immediately if wear exceeds limits; failure to do so can easily lead to catastrophic accidents involving trailer detachment.
Trailer Axle Assembly
Axles bear the vehicle's weight and fall into two mainstream categories: American-style and German-style. American-style axles offer high cost-effectiveness, robust heavy-load capacity, and excellent parts interchangeability, making them suitable for short-haul, heavy-load transport of materials like sand, gravel, and coal. German-style axles feature superior heat dissipation, even tire wear, and high stability at highway speeds; they are well-suited for long-haul, standard-load line-haul logistics, offering distinct advantages in lightweight design and energy efficiency. Internally, an axle assembly comprises the axle beam, wheel hub, bearings, and brake drums or discs. Braking systems are categorized into drum and disc types; under current regulations, disc brakes are increasingly being adopted for trailers used in hazardous material transport and standard-load long-haul operations, as they provide faster braking response and better heat dissipation.
Suspension systems primarily fall into two categories:
leaf spring suspension and air suspension. Leaf spring suspension consists of leaf spring stacks, U-bolts, and balance arms; it relies on the deformation of the steel plates to absorb shock. Featuring a simple, durable design and low maintenance costs, it remains the most widely used configuration in the market. In contrast, air suspension utilizes air bellows for cushioning and shock absorption and offers automatic vehicle height adjustment. It delivers superior damping performance-protecting sensitive cargo and reducing chassis wear-and has seen a steady rise in adoption rates in recent years, particularly for applications involving the transport of fresh produce (via "Green Channels") and precision equipment. The core function of the suspension system is to balance loads across the three axles; by distributing forces during travel over uneven terrain, it prevents individual axles from becoming overloaded, thereby avoiding damage to axles and tires.
Braking System Components：
A complete air brake system assembly includes brake chambers, brake shoes, brake drums, relay valves, air reservoirs, and brake hoses. Trailers rely on high-pressure air supplied by the tractor unit to actuate the brakes; the relay valve regulates the speed of air supply, while the air reservoir stores high-pressure air to ensure parking brake functionality. Brake shoes are high-wear components that require inspection every 3 to 6 months under heavy-load conditions. Brake drums exhibiting scoring or loss of roundness must be either refinished (bored out) or replaced. Air leaks and uneven braking (brake pull) are the most common issues encountered with trailer braking systems.
Industry Trends and Key Points for Maintenance and Servicing
Lightweighting upgrades: High-strength steel frames, aluminum alloy wheels, and air suspension systems are progressively replacing traditional, heavy steel components; this reduces the vehicle's curb weight and increases cargo capacity, aligning with regulations on overloading and the need for fuel efficiency.
Adoption of smart technologies: Installation rates for tire pressure monitoring systems, onboard GPS tracking, and intelligent braking warning systems are rising year by year, facilitating remote fleet management.
Key maintenance priorities: Regularly greasing kingpins, lubricating landing gear gears, retightening suspension U-bolts, and checking the braking system monthly for air leaks; replacing wear-and-tear parts proactively to prevent breakdowns on the road.
Export trends: There is immense demand in African, Southeast Asian, and South American markets; components must comply with local load standards and certification requirements, with kingpins, axles, and landing gear being the three categories with the highest export volumes.
