Overview
ISO 21069-2:2008 specifies a standardized procedure for assessing the service braking performance of heavy road vehicles (maximum authorized total mass > 3.5 t) equipped with air-over-hydraulic (A/H) and purely hydraulic braking systems using a roller brake tester. The standard ensures comparable measurement results across test locations so braking efficiency and pass/fail decisions can be made reliably for vehicles in service, including those with Electronic Braking Systems (EBS).
Key topics and technical requirements
- Scope and purpose: Establishes a repeatable roller brake test method for vehicle categories M2, M3, N2, N3, O3 and O4; not applicable to passenger cars.
- Definitions and symbols: Standardizes terminology (braking force, braking force imbalance, braking rate) and symbols used in calculations.
- Test methods and conditions: Details vehicle preparation (clean rollers/tyres, tyre pressures per manufacturer), measurement points, laden and partly laden test approaches, and real‑time simultaneous measurement of actuator pressure and brake force.
- A/H and hydraulic provisions: Describes conversion between pneumatic and hydraulic pressures via A/H converters and treatment of load‑sensing valves; allows extrapolation methods (e.g., two‑point or laden measurement) to predict laden braking performance without intrusive hydraulic transducers.
- Equipment accuracy and design: Annex A lists roller brake tester technical requirements - roller diameter (min 200 mm; 150 mm for some on‑ground testers), roller length (min 900 mm), accommodation for tyre diameters 530–1 300 mm, and maximum axle load ratings (up to 13 000 kg).
- Data recording and reporting: Specifies required test report content (vehicle ID, axle loads, measured braking forces, actuator/control line pressures, imbalance/variation, tester model/version/serial).
- Assessment criteria: Defines presentation of results and criteria for pass/fail evaluation referenced to legal requirements (e.g., UNECE Regulation No. 13 for guidance).
Practical applications
- Ensures consistent, legally defensible brake efficiency testing during periodic technical inspection and workshop diagnostics.
- Enables inspection stations and test labs to validate service brake performance for heavy commercial vehicles, trailers and buses.
- Supports manufacturers and test equipment suppliers in calibrating and certifying roller brake testers to meet international expectations.
- Useful for regulatory bodies, technical services and certification agencies implementing or harmonizing brake testing protocols.
Who should use this standard
- Vehicle inspection authorities and periodic technical inspection (PTI) centres
- Brake and vehicle manufacturers
- Roller brake tester designers, suppliers and calibration labs
- Regulatory agencies and technical services for compliance verification
Related standards
- ISO 21069-1 (pneumatic braking systems)
- UNECE Regulation No. 13 (reference for performance criteria and periodic inspections)
Keywords: ISO 21069-2:2008, roller brake tester, braking systems, air over hydraulic, hydraulic braking, braking efficiency, heavy vehicles, brake testing, UNECE Regulation No. 13.
Open preview (PDF)Road vehicles — Test of braking systems on vehicles with a maximum authorized total mass of over 3,5 t using a roller brake tester — Part 2: Air over hydraulic and purely hydraulic braking systems
