Overview
ISO 1726-2:2007 - Road vehicles: Mechanical couplings between tractors and semi-trailers (Part 2) defines dimensional and operating requirements to ensure interchangeability between low-coupling tractors and high-volume semi-trailers. The standard specifies gooseneck contour geometry, fifth-wheel heights, clearance zones and articulation/tilt angle limits so that a low-coupling tractor and a high-volume semi-trailer can form a compatible high-volume articulated vehicle. ISO 1726-2:2007 does not set mass or overall dimension limits (these remain subject to legislation).
Key topics and technical requirements
- Fifth wheel height
- Laden tractor: height h = 900 mm to 975 mm above ground.
- Uncoupled tractor: h shall not exceed 1 000 mm.
- Forward clearance / gooseneck contour
- Forward clearance radius r = 2 040 mm from kingpin axis; optimized gooseneck surface defined by planes and a surface of revolution.
- Internal generator values include plane lengths (e.g., 500 mm, 1 350 mm, 1 800 mm), arc radius 450 mm, and radius between kingpin axis and vertical gooseneck portion 2 100 mm.
- Angles of generator surfaces: γ = 1° and 7°, inclined plane α ≈ 3.5°.
- Operating angles and clearances
- Maximum inclination of semi-trailer relative to tractor: front ω ≤ 3.5°, rear ω ≤ 4.5°.
- Lateral inclination δ ≤ 2° without contact.
- Articulation angle ϕ: design must avoid contact with tyres or equipment for ϕ up to 25°; under manoeuvring ϕ must reach 90°, with ω reducing from 4.5° to 3° as ϕ varies 25°→90°.
- Free space parameters
- Minimum clearances between defined cylinders/surfaces: L ≥ 100 mm and another design clearance L ≥ 80 mm at specified reference points.
Applications and users
ISO 1726-2:2007 is used by:
- Tractor and semi-trailer manufacturers for design and dimensional compliance (low-coupling tractors and high-volume semi-trailers).
- Component suppliers (fifth-wheel, kingpin, gooseneck designers) to ensure mechanical coupling compatibility.
- Fleet engineers and systems integrators to verify interchangeability between tractors and trailers in mixed fleets.
- Test laboratories and certification bodies to assess clearance, articulation and interference during type approval or conformity checks.
- Regulators and standardization teams as a reference for compatibility requirements (while legal mass/dimension limits are set by legislation).
Practical benefits include reduced coupling interference, predictable articulation behaviour, and improved cross-manufacturer interchangeability for high-volume articulated vehicles.
Related standards
- ISO 1726-1 - Interchangeability between tractors and semi‑trailers for general cargo (other part of the ISO 1726 series).
- ISO 337 - Fifth-wheel coupling pin dimensions (referenced for kingpin basics and interchangeability).