ISO 9815:2024

Overview

ISO 9815:2024 - Road vehicles: Passenger-car and trailer combinations - Lateral stability test - defines a repeatable, discriminatory test method to quantify the lateral stability (yaw damping) of passenger-car and light-truck towing-vehicle–trailer combinations. The fourth edition updates the 2010 version and specifies how to excite a combination with a defined steering impulse, measure the resulting yaw oscillation, and determine damping behaviour across several constant speeds. A steady-state circular test is included where non-periodic instability is of interest.

Keywords: ISO 9815:2024, lateral stability test, passenger-car and trailer combinations, yaw oscillation, steering impulse, vehicle dynamics.

Key topics and requirements

• Test objective: Determine the damping characteristic of the yaw articulation angle between towing vehicle and trailer after a single steering impulse while steering is then held fixed.
• Test setup: Combination driven in steady-state, straight-ahead condition prior to excitation; tests executed at multiple constant speeds.
• Measurement variables: Steering-wheel angle, towing-vehicle longitudinal velocity, trailer lateral acceleration, yaw articulation angle. Yaw velocities of towing vehicle and trailer are recommended.
• Data analysis: Damping of oscillation, yaw velocity ratio, zero-damping and reference-damping speeds, and presentation of test results and conditions.
• General conditions: Conformity with ISO 15037-1 (general vehicle dynamics test conditions), with additions:
  • Test track mean gradient G recorded and maintained within ±0.01.
  • Test surface minimum width: 8 m (with increased run-off area recommended).
  • Wind velocity should not exceed 2.5 m/s.
  • Instrumentation and driver combined mass should not exceed 150 kg and be arranged to minimize inertia effects.
  • Transducer accuracy example: articulation angle ±0.2° recommended.
• Optional tests: A steady-state circular test is specified where non-periodic instability needs assessment.

Applications and who uses it

• Vehicle manufacturers and chassis/trim engineers assessing towing stability and trailer behaviour.
• Automotive test houses and certification bodies conducting dynamics validation and comparative testing.
• R&D teams investigating trailer hitch design, load distribution, and active safety systems affecting yaw damping.
• Regulators and safety analysts correlating vehicle-trailer dynamic characteristics with handling and accident risk (note: the standard cautions that correlations with accident statistics require additional evidence).

Related standards

• ISO 15037-1:2019 - General conditions for passenger-car dynamics tests (normative reference).
• ISO 3833 - Vehicle type definitions and classifications.
• ISO 8855, ISO 2416 - Vehicle dynamics vocabulary and mass distribution references.

ISO 9815:2024 is an essential reference for standardized lateral stability testing of passenger-car and light-truck trailer combinations, supporting objective evaluation of yaw damping and handling behaviour.