Typically, small, medium, and large transport tractors are classified by engine power (≤30 hp, 30 - 100 hp, and 100 - 200 hp respectively, i.e., ≤22.1 kW, 22.1 - 73.5 kW, and 73.5 - 147.0 kW). Standards for them differ significantly across countries and regions in terms of external dimensions, braking performance, safety protection, and emissions.
China Transport Tractors
Chinese standards mainly rely on mandatory national standards, with clear distinctions in size and braking performance based on power, and unified basic safety requirements.
Small transport tractors (≤22.1 kW)
Overall dimensions: For wheeled models with engine power ≤58 kW (covering small ones), the length of the transport unit shall not exceed 10m, width ≤2.5m, and height ≤3m. For walking - type small transport tractors, the unit length shall not exceed 5m, width ≤1.7m, and height ≤2.2m.
Braking performance: When braking at an initial speed of 20 km/h, both full - load and no - load braking distances of walking tractor transport units shall not exceed 6.5m, and the test channel width is 2.3m.
Safety requirements: Comply with GB 18447.2. Key parts such as the steering handle and traction connection components must meet safety indicators to prevent loss of control during short - distance transportation.
Medium transport tractors (22.1 - 73.5 kW)
Overall dimensions: It also falls into the category of ≤58 kW or close to 58 kW. The length of the transport unit is generally within 10m, and the width and height are the same as those of small wheeled transport tractors, i.e., ≤2.5m and ≤3m respectively.
Braking performance: For medium wheeled transport tractors, when braking at an initial speed of 20 km/h, the full - load braking distance shall not exceed 6.5m, and the no - load braking distance shall not exceed 6.0m, with a test channel width of 3.0m.
Safety and emissions: It must be equipped with safety frames, fire extinguishers, and warning signs in the cab. Emissions must meet the pollutant limits in GB 20891 (China's Stage III and IV standards). Meanwhile, dangerous parts need protective devices and safety signs in accordance with GB 18447.1.
Large transport tractors (73.5 - 147.0 kW)
Overall dimensions: For wheeled models with engine power >58 kW, the length of the transport unit can be extended to 12m, while the width remains ≤2.5m and the height can be increased to 3.5m, adapting to the demand for larger transportation capacity.
Safety and emissions: The body frame strength and transmission system protection level are more strictly required. The noise at the driver's position must meet the limits of GB 6376.
The exhaust emissions must meet higher - level non - road diesel engine standards to reduce pollutants such as carbon monoxide and hydrocarbons.
European Union
The EU uniformly regulates transport tractors through regulations such as (EU) No 167/2013, and the standards are differentiated by vehicle category, with supplementary requirements for different power levels in terms of emissions and safety structures.
Small transport tractors
Safety standards: Comply with the general safety requirements of wheeled tractor category T and tracked tractor category C in (EU) No 167/2013, including basic structural integrity and operator space requirements. For small variable - reach transport tractors, refer to EN 1459 - 4, which specifies safety verification requirements for load - handling.
Emission standards: Meet the pollutant limit requirements of EU Stage V. Due to their small power, the emission control focuses on particulate matter and nitrogen oxides, matching the emission control technologies of small non - road mobile machinery.
Medium transport tractors
Safety standards: In addition to the basic safety requirements like roll - over protective structures (ROPS) and emergency stop devices, the visibility of the cab and the reliability of the braking system are further regulated. If towing a trailer, the connection part must comply with the Machinery Directive 2006/42/EC to avoid separation accidents during transportation.
Compatibility requirements: Follow EN 1726 - 1 standards to ensure the interchangeability of connecting dimensions with semi - trailers, facilitating the matching of medium - capacity trailers for cargo transportation.
Large transport tractors
Safety standards: For large wheeled tractors of subcategory T1 or T2, the structural strength requirements are higher. ROPS and falling - object protective structures (FOPS) must pass stricter impact tests to cope with the greater impact force during roll - over or falling - object incidents of large vehicles.
Emission and noise: The emission test procedures are more complex, requiring compliance with the detailed test requirements of (EU) 2016/1628. At the same time, stricter limits are imposed on internal and external noise to reduce environmental impact during high - power operation.
United States
U.S. standards emphasize braking and protective structure safety. There are unified mandatory requirements for tractors above 20 hp, and differentiated weight and axle load standards for large transport tractors.
Small transport tractors (>20 hp, ≤22.1 kW)
Protective structures: Although they are small, if the engine power exceeds 20 hp, they must be equipped with ROPS and seat belts meeting SAE J4C standards. The seat belt anchorages must withstand a static tensile load of 453.6 kg to ensure the driver's safety in case of roll - over.
Weight requirements: When configuring ROPS, ballast should be added if necessary. The minimum total weight should reach 50 kg per maximum power - take - off horsepower, and the front - end weight should be at least 25% of the test weight of the tractor.
Medium transport tractors (22.1 - 73.5 kW)
Braking and protection: It also needs to meet the ROPS and seat belt standards of 29 CFR Part 1928. For medium transport tractors used in highway transportation, the axle load must comply with federal standards, with a single - axle load not exceeding 9072 kg and a tandem axle load not exceeding 15422 kg.
Basic performance: The braking system should ensure that the vehicle can stop stably under medium - load conditions, laying the foundation for adapting to short - and medium - distance bulk cargo transportation.
Large transport tractors (73.5 - 147.0 kW)
Weight and axle load: When traveling on the interstate highway system, the total weight shall not exceed 36287 kg. The bridge formula is also applicable, which may reduce the maximum allowable total weight according to the axle spacing to avoid damaging highway bridges.
Braking performance: Refer to 49 CFR Part 571. When loaded to the rated total mass and traveling at 96.6 km/h, the braking distance should not exceed 76.2 meters, ensuring the safety of large - capacity and high - speed transportation.
