ISO 1726-2:2007

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).