Comprehensive Guide to Semi-Trailer Landing Gear: From Fundamental Specifications to Selection and Application

Comprehensive Guide to Semi-Trailer Landing Gear: From Fundamental Specifications to Selection and Application

Updated: February 10, 2026
Editor: Administrator
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In the semi-trailer transportation and operational system, landing gear—serving as the primary supporting device for the front load of a semi-trailer after decoupling from the tractor—directly impacts parking stability, loading and unloading safety, and operational efficiency. Based on the product standards of enterprises such as Liangshan Zhongxing Machinery, combined with industry technical specifications and innovative applications, this article systematically reviews the core knowledge of semi-trailer landing gear from definition, classification, parameters, and standards to selection and matching, providing professional reference for industry practitioners.

I. Core Definition and Functional Positioning of Landing Gear

Semi-trailer landing gear (commonly referred to as the “supporting device”) is the critical component that independently supports the front load of a semi-trailer once separated from the tractor unit. Its primary functions encompass three key dimensions:

Load Bearing: Distributes the front weight of the semi-trailer through high-strength structural design to prevent frame deformation.

Height Adjustment: Adapts to varying ground heights at loading and unloading sites through telescopic mechanisms to ensure trailer leveling.

Stability Assurance: Works in conjunction with anti-slip footplates to prevent tilting or sliding during parking or cargo operations.

According to the industry standard JT/T 475 Trailer Supporting Devices, landing gear must comply with requirements regarding rated dynamic load, stroke accuracy, operating force, and other technical specifications, serving as the “first line of defense” for safe semi-trailer operation.

II. Classification System: Structural and Operational Dimensions

Landing gear classification is primarily based on structural configuration and operating mechanism, with each type suited to different application scenarios.

(1) Structural Type: External vs. Internal Gearbox Designs

External Type (American Style):
Characterized by a gearbox mounted externally on the outer tube, this is the mainstream market configuration, accounting for over 70% of sales.

Advantages: Simple structure, convenient maintenance, quick gearbox replacement.

Disadvantages: Larger overall dimensions, occupying external chassis space.

For example, a 28-ton / 480mm stroke external landing gear model features:

Single-speed weight: 103 kg

Two-speed (linked) weight: 98 kg

Low-speed travel per revolution: 0.75 mm/r

High-speed travel per revolution: 6 mm/r

It is suitable for general freight operations requiring stable load capacity and easy maintenance.

Internal Type (German Style):
Features an integrated gearbox within the outer tube, resulting in a more compact structure and 10–15% lower weight compared to equivalent external types.

For instance, a 25-ton / 480mm internal model weighs:

Single operation: 90 kg

Linked operation: 89 kg

High-speed travel: 7.5 mm/r

While more efficient and lightweight, maintenance requires disassembly of the outer tube, making it better suited for applications with strict weight and space constraints, such as refrigerated trailers and container transport.

(2) Operational Mode: Single-Action vs. Linked Systems

Single-Action Landing Gear:
Each leg operates independently.

Advantage: Flexible adjustment on uneven ground (construction sites, mining areas).

Disadvantage: Lower efficiency; requires repeated adjustments or dual operation.

Linked Landing Gear:
Both legs operate synchronously via a mechanical linkage.

Over 50% higher operational efficiency

Better height consistency

Reduced frame torsion risk

Linked systems are ideal for standardized logistics hubs and port operations with frequent loading cycles.

Additionally, hydraulic landing gear (pneumatic-hydraulic or electro-hydraulic) is increasingly applied in heavy-duty trailers exceeding 40 tons, reducing manual labor intensity.

III. Key Technical Parameters

(1) Rated Load

Rated load includes:

Dynamic Load: Load during lifting/lowering.

Static Load: Sustained load during parking.

Common dynamic load ratings: 10T, 16T, 25T, 28T.

28T models are standard for 13-meter general freight trailers (static load up to 80T).

10–16T models suit light-duty refrigerated trailers.

A safety factor of 1.25× is recommended to prevent overload-related damage.

(2) Stroke and Dimensions

Stroke (430mm or 480mm standard) determines height adjustment range.
480mm is most widely used due to broader terrain compatibility.

Material specifications typically include:

Outer tube: 130×130×3.75mm Q345B steel

Inner tube: 120×120×3.75mm Q235 steel

These balance structural strength and weight control.

(3) Foot Type and Travel per Revolution

Foot types: A, G, R, S, T.

T-type foot (≈200×150mm contact area) dominates 80% of the market due to superior stability.

S-type foot is suitable for muddy terrain.

Travel per revolution:

External type: 0.75 mm/r (low speed), 6 mm/r (high speed)

Internal type: 0.83 mm/r (low speed), 7.5 mm/r (high speed)

High-frequency logistics operations benefit from faster travel rates; precision transport requires fine adjustment.

IV. Standards and Model Identification

(1) Compliance Standards

Domestic products must comply with JT/T 475.
Export products may require compliance with ECE R55 and RoHS standards, including ≥100,000-cycle fatigue testing.

Key requirements include:

Safety locking mechanism

Operating force limits (≤150N single, ≤95N linked)

Dimensional tolerance within ±0.1mm

(2) Model Coding

Typical format:
Enterprise Code – Type – Rated Load – Foot Type – Height Parameter

Example: ZX-L28-T25

ZX: Manufacturer code

L: Linked type

28: 28-ton dynamic load

T: T-type foot

25: Height parameter (250mm)

V. Core Components and Innovative Applications

(1) Core Components

Lead Screw: Φ36–Φ38mm, 40Cr or 45# steel, quenched and tempered

Nut: Ductile iron Q600-2 or forged steel

Gear: 20CrMnTi carburized, HRC58–62

Thrust Bearing: ≥50kN axial capacity

Tube Material: Q345B or Q235

(2) PE Support Pads (HDPE)

Compressive strength: 80–200 MPa

Single-pad capacity: up to 150T

1/8 the weight of steel plates

Anti-slip design with extended service life (>5 years)

Widely used in crane lifting, wind turbine installation, and heavy-duty construction.

Additionally, heavy-duty trailers may incorporate a fifth support leg to distribute lateral loads and enhance operational stability.

VI. Selection and Maintenance

(1) Selection Principles

Compatibility:
Match rated load and stroke to trailer type and operating environment.

Safety:
Ensure compliance with JT/T 475; verify material quality and heat treatment.

Cost Efficiency:
Avoid over-specification for light-duty applications or under-specification for heavy-duty use.

(2) Maintenance Guidelines

Weekly inspection (daily in heavy-duty use)

Monthly lubrication with lithium-based grease (-20°C to 120°C)

Anti-corrosion protection in coastal or chemical environments

Replace worn components (lead screws: 3–5 years typical lifespan)

VII. Industry Trends

Lightweighting: Adoption of high-strength steel (Q690) and aluminum alloys, reducing weight by 15–20%.

Intelligent Monitoring: Integrated load and height sensors with overload alerts.

Standardization: Unified interchangeability standards to improve compatibility across brands.

Conclusion

Although landing gear may appear to be a minor component, it plays a decisive role in operational safety, cargo integrity, and efficiency. From structural classification to parameter selection and maintenance management, a scientific understanding of landing gear ensures optimized performance and long-term reliability.

As the semi-trailer industry advances toward higher efficiency, sustainability, and safety standards, landing gear systems will continue evolving toward lightweight, intelligent, and standardized solutions—providing stronger support for high-quality development in commercial transportation.