ISO 1726-3:2023

Road vehicles - Mechanical couplings between tractors and semi-trailers - Part 3: Requirements for semi-trailer contact area to fifth wheel

This document specifies the test conditions of a static test performed on the semi-trailer contact area to the fifth wheel. It ensures the suitability of the semi-trailer to couple the greatest possible variety of tractor vehicles equipped with a fifth wheel coupling in accordance with ISO 3842. It also specifies requirements to avoid damages or malfunctions of the fifth wheel coupling caused by the semi-trailer chassis, the semi-trailer plate or any other of its components.

Véhicules routiers — Liaisons mécaniques entre tracteurs et semi-remorques — Partie 3: Exigences pour plateaux à friction de semi-remorques

General Information

• Status: Published
• Publication Date: 26-Jul-2023
• 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/WG 1 - Mechanical couplings
• Current Stage: 6060 - International Standard published
• Start Date: 27-Jul-2023
• Due Date: 17-Oct-2022
• Completion Date: 27-Jul-2023

Relations

• Revises: ISO 1726-3:2010 - Road vehicles - Mechanical couplings between tractors and semi-trailers - Part 3: Requirements for semi-trailer contact area to fifth wheel
• Effective Date: 23-Apr-2020

Overview

ISO 1726-3:2023 specifies requirements and test methods for the semi‑trailer contact area to the fifth wheel. The standard defines static test conditions and acceptance criteria to ensure semi‑trailers are compatible with a wide variety of tractor vehicles fitted with fifth wheel couplings in accordance with ISO 3842. Its purpose is to prevent damage or malfunction of the fifth wheel caused by the semi‑trailer chassis, plate or related components.

Key topics and requirements

• Scope of test: Static verification of the semi‑trailer contact area (area centred on the kingpin) using a homogeneously distributed vertical load based on the trailer manufacturer’s declared maximum static load (test load).
• Deflection and flatness limits:
  • Maximum overall vertical deflection during the static test: S ≤ 3.5 mm relative to the plane spanned by top surfaces of the support blocks.
  • For calculation (elastic deformation only): S ≤ 1.5 mm.
  • Total unevenness before and after test: ≤ 2 mm at any point within the contact zone.
• Test arrangement and procedure:
  • Test performed on whole semi‑trailer or representative section; fixing must follow kingpin manufacturer’s fitting instructions.
  • Test forces include a safety factor of 2 to cover dynamic influences.
  • Load applied over a defined application area (figures in the standard).
• Support block geometry and placement:
  • Support blocks: L = 240 mm, W = 140 mm, positioned 580 mm from kingpin centre (left and right).
  • Minimum block height H = 95 mm; blocks must feature chamfers (max 5 mm × 30°) and corner radius R = 10 mm to avoid unrealistic local stresses.
• Design constraints for contact area:
  • No protrusions or sharp edges in the contact area; holes with sharp edges or holes > 50 mm diameter are prohibited.
  • Contact area diameter when coupled: minimum 965 mm (figures detail minimum dimensions).

Applications and users

ISO 1726-3:2023 is used by:

• Semi‑trailer manufacturers and chassis designers to ensure fifth wheel compatibility and to incorporate acceptable stiffness and flatness into designs.
• Test laboratories and certification bodies conducting static verification or validating calculation models against physical tests.
• Fifth wheel and kingpin manufacturers, to understand interface requirements and avoid mating‑piece damage.
• Fleet operators, maintenance teams and regulatory authorities concerned with safe coupling, durability and interchangeability between tractors and trailers.

Benefits include improved interoperability, reduced wear/damage to fifth wheel couplings, and clearer acceptance criteria for design validation and conformity assessment.

Related standards

• ISO 3842 - Fifth wheels - Interchangeability (referenced for fifth wheel coupling dimensions and compatibility).

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 1726-3
Second edition
2023-07
Road vehicles — Mechanical couplings
between tractors and semi-trailers —
Part 3:
Requirements for semi-trailer contact
area to fifth wheel
Véhicules routiers — Liaisons mécaniques entre tracteurs et semi-
remorques —
Partie 3: Exigences pour plateaux à friction de semi-remorques
Reference number
© ISO 2023
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
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Phone: [phone]
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Website: www.iso.org
Published in Switzerland
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Requirements . 1
5 Test methods . 2
5.1 General . 2
5.2 Test with static vertical force . 2
5.2.1 Test arrangement . 2
5.2.2 Test procedure. 2
5.3 Alternative method . 2
6 Design of the semi-trailer contact zones to the fifth wheel . 5
Bibliography . 7
iii
Foreword
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This document was prepared by Technical Committee ISO/TC 22, Road vehicles, Subcommittee SC 40,
Specific aspects for light and heavy commercial vehicles, busses and trailers.
This second edition cancels and replaces the first edition (ISO 1726-3:2010), which has been technically
revised
The main changes are as follows:
— modification of maximum displacement and load application in Clause 4;
— modification of static test requirements in Clause 5.
A list of all parts in the ISO 1726 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
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iv
Introduction
The dimensional interchangeability of truck and trailer is specified in various standards and
regulations. In order to be able to
...