Overview
ISO 22139:2022 defines a standardized test method for steering effort measurement when manoeuvring at low speed or with the vehicle stationary. It is aimed primarily at heavy commercial vehicles and buses (vehicle categories M3, N2, N3 by ECE/EC classification) and can also be applied to smaller trucks and buses (M2, N1). The standard quantifies driver perception of steering feel and effort by measuring steering-wheel angle, torque and speed and deriving characteristic parameters for objective evaluation.
Key topics and technical requirements
- Scope and application: Low-speed or stationary manoeuvres for trucks and buses; main focus on vehicles exceeding 3.5 t (trucks) and 5 t (buses/articulated buses).
- Measured variables (Clause 5): steering-wheel angle (δ), steering-wheel torque (M), and steering-wheel speed (dδ/dt).
- Characteristic parameters (Clause 4 & 9):
- Steering-wheel torque (including maximum torque and catch-up behaviour)
- Steering-wheel work (energy required to turn between defined angles)
- Steering-wheel return ability (ability to return toward straight ahead without input)
- Steering-wheel torque variation (∆M/Mmax)
- Measuring equipment (Clause 6): multi-channel recorder, appropriate transducers and preferably a steering machine with driver emergency override. The standard specifies typical operating ranges and recommended maximum errors (e.g., steering-wheel angle range ±1 000° ±1°, torque ±30 Nm ±0.3 Nm, speed ±600°/s ±2°/s).
- Test conditions and procedure (Clauses 7–8): defined test track layouts for low-speed manoeuvres and stationary tests, vehicle preparation and warm-up, tyre/rim/vehicle loading conditions, and data processing requirements.
- Reporting: normative test-report formats and required data are provided in Annexes A and B.
Practical applications
- Objective evaluation of steering feel during tight turns, parking, and low-speed operations.
- Design and validation of steering systems (hydraulic, electric-hydraulic, or electric power steering) to ensure acceptable driver effort and comfort.
- Comparative testing for supplier validation, component tuning, or quality control.
- Regulatory and compliance testing where objective steering-effort metrics are required.
- Fleet operators and ergonomics teams assessing driver workload for operational improvements.
Who uses this standard
- Vehicle manufacturers (OEMs) and chassis engineers
- Steering system and component suppliers
- Automotive test laboratories and R&D teams
- Certification bodies and regulators
- Fleet safety and ergonomics specialists
Related standards
- ISO 15037-2 (vehicle dynamics test methods - general conditions for heavy vehicles and buses)
- ISO 8855 (vehicle dynamics vocabulary)
ISO 22139:2022 provides a repeatable, measurable framework for assessing steering effort at low speeds, helping engineers and testers optimize steering systems for safety, comfort, and regulatory compliance.