ISO 1726-2:2007

Road vehicles - Mechanical couplings between tractors and semi-trailers - Part 2: Interchangeability between low-coupling tractors and high-volume semi-trailers

ISO 1726-2:2007 specifies dimensions to ensure interchangeability between a low coupling height tractor vehicle and a coupled high-volume semi-trailer, the two together constituting a high-volume articulated vehicle. It specifies certain interchangeability dimensions, including those of the optimised gooseneck contour, as well as operating dimensions related to angle values. The specifications are primarily intended to permit semi-trailers to be coupled with two-axle tractors. However, three-axle tractors are not excluded, provided they are in compliance with the requirements of ISO 1726-2:2007. ISO 1726-2:2007 does not provide limitations of maximum gross mass and overall dimensions, which are generally laid down by legislative requirements.

Véhicules routiers — Liaisons mécaniques entre tracteurs et semi-remorques — Partie 2: Interchangeabilité entre tracteurs avec accouplement bas et semi-remorques de grand volume

General Information

• Status: Published
• Publication Date: 18-Apr-2007
• ICS: 43.040.70 - Couplings
• Technical Committee: ISO/TC 22/SC 40 - Specific aspects for light and heavy commercial vehicles, busses and trailers
• Drafting Committee: ISO/TC 22/SC 40 - Specific aspects for light and heavy commercial vehicles, busses and trailers
• Current Stage: 9093 - International Standard confirmed
• Start Date: 18-Jul-2022
• Completion Date: 13-Dec-2025

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).

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 1726-2
First edition
2007-04-15
Road vehicles — Mechanical couplings
between tractors and semi-trailers —
Part 2:
Interchangeability between low-coupling
tractors and high-volume semi-trailers
Véhicules routiers — Liaisons mécaniques entre tracteurs et semi-
remorques —
Partie 2: Interchangeabilité entre tracteurs avec accouplement bas et
semi-remorques de grand volume

Reference number
©
ISO 2007
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ii © ISO 2007 – All rights reserved

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
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International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 1726-2 was prepared by Technical Committee ISO/TC 22, Road vehicles, Subcommittee SC 15,
Interchangeability of components of commercial vehicles and buses.
ISO 1726 consists of the following parts, under the general title Road vehicles — Mechanical couplings
between tractors and semi-trailers:
1)
⎯ Part 1: Interchangeability between tractors and semi-trailers for general cargo
⎯ Part 2: Interchangeability between low-coupling tractors and high-volume semi-trailers

1) Revision of ISO 1726:2000.
INTERNATIONAL STANDARD ISO 1726-2:2007(E)

Road vehicles — Mechanical couplings between tractors and
semi-trailers —
Part 2:
Interchangeability between low-coupling tractors and
high-volume semi-trailers
1 Scope
This part of ISO 1726 specifies dimensions to ensure interchangeability between a low coupling height tractor
vehicle and a coupled high-volume semi-trailer, the two together constituting a high-volume articulated vehicle.
It specifies certain interchangeability dimensions, including those of the optimised gooseneck contour, as well
as operating dimensions related to angle values. The specifications are primarily intended to permit
semi-trailers to be coupled with two-axle tractors. However, three-axle tractors are not excluded, provided they
are in compliance with the requirements of this part of ISO 1726.
This part of ISO 1726 does not provide limitations of maximum gross mass and overall dimensions, which are
generally laid down by legislative requirements.
2 Interchangeability dimensions
2.1 Height of fifth wheel of a laden tractor
The height, h, of the fifth wheel of a laden low-coupling tractor above ground (see Figure 1) shall be in the
range 900 mm to 975 mm.
Key
h height of fifth wheel
Figure 1 — Height of fifth wheel
2.2 Height of fifth wheel of an uncoupled tractor
The height, h, of the fifth wheel of an uncoupled low-coupling tractor shall not exceed 1 000 mm.
2.3 Forward clearance zone radius of a semi-trailer
The front end of the semi-trailer (see Figure 2) shall not exceed the radius, r , of 2 040 mm.
Dimensions in millimetres
Key
L distance between two cylinders of revolution [see 3.4 a)]
L distance between surface of cylinder of revolution and conical surface of revolution [see 3.4 b)]
r forward clearance zone radius of semi-trailer (see 2.3)
r radius between axis of coupling pin and lower part of the semi-trailer gooseneck [see 2.4 d)]
ω angle of inclination towards the front
ω angle of inclination towards the rear
ϕ angle of articulation
Figure 2 — Free space between tractor and semi-trailer
2 © ISO 2007 – All rights reserved

2.4 Gooseneck contour
The gooseneck shall be located on the outside of a surface consisting of different planes and one surface of
revolution
...