Overview
ISO 8717:2000 - "Commercial road vehicles - Fifth wheel couplings - Strength tests" specifies the strength test conditions and pass/fail requirements for 50 mm and 90 mm fifth wheel couplings used on commercial road vehicles. The standard defines how to mount couplings on a test bed, how to determine the coupling D‑value, and the static and dynamic loads (including special provisions for forced semi‑trailer axle steering in Annex A).
Key topics and requirements
- Scope: Strength tests for 50 and 90 fifth wheel couplings (see ISO 3842 for interchangeability).
- D‑value calculation: The standard gives a D‑value calculation based on vehicle masses and vertical load. Variables include the towing vehicle design mass, the semi‑trailer design mass, the vertical mass on the coupling and g = 9.81 m/s².
- Mounting and test bed: Couplings must be fixed to the test bed as they would be on the vehicle, using the manufacturer’s fitting instructions; flexible components may be neutralized at manufacturer’s discretion.
- Static lifting test:
- Apply vertical lifting up to F = g·U; coupling plate must show no major permanent bending over more than 0.2% of its width.
- For 50 mm type: kingpin must not separate at F = g·2.5·U.
- For 90 mm type: kingpin must not separate at F = g·1.6·U (minimum 500 kN).
- Loading lever applied 1.0–1.5 m from kingpin centre at 90° to entry direction.
- Dynamic test:
- Simultaneous vertical and horizontal loads applied sinusoidally.
- Vertical pulsating load: between 0.4·U·g and 1.2·U·g via a rigid counter‑plate; friction between plates limited (μ ≤ 0.15).
- Horizontal alternating load: between ±0.6·D (Annex A: ±0.675·D for forced steering).
- Frequency limited to ≤ 35 Hz and chosen to avoid system natural frequency; the vertical and horizontal cycle rates differ by 1–3%.
- The dynamic test must not cause permanent deformation, cracks or breaks.
- Annex A (normative): Additional dynamic and static tests and an extra moment load for fifth wheels intended to accept steering wedges; limited permanent deformation (up to 0.5%) allowed but no cracking.
Applications and users
ISO 8717 is used by:
- Fifth wheel and coupling manufacturers for design verification and type testing.
- Commercial vehicle OEMs and chassis builders for supplier specification and installation checks.
- Independent test laboratories and certification/approval authorities performing strength and conformity tests.
- Fleet operators and safety engineers evaluating coupling performance and compatibility.
Related standards
- ISO 3842 - Fifth wheels - Interchangeability (mounting and interface dimensions).
- ISO 1176 - Road vehicles - Masses - Vocabulary and codes (definitions of masses used in D‑value).
Keywords: ISO 8717:2000, fifth wheel couplings, strength tests, D‑value, static lifting test, dynamic test, commercial road vehicles, forced axle steering.
