Overview
ISO 13325:2019 - Tyres: Coast-by methods for measurement of tyre-to-road sound emission defines standardized test methods to measure tyre-to-road noise when a vehicle is in free-rolling, non‑powered (coast-by) operation. The procedure is applicable to passenger cars and commercial vehicles (as defined in ISO 3833) and produces objective, repeatable sound emission data for tyres fitted on a moving test vehicle. It is not intended to measure tyre noise under powered driving or to assess traffic noise at a specific location.
Key topics and technical requirements
- Coast-by condition: Vehicle in neutral or equivalent, engine and non-essential auxiliaries switched off to ensure free-rolling measurement of tyre noise.
- Test site and surface: Test area and pavement must meet the requirements of ISO 10844 (dry, clean, defined geometry; no large reflective objects near the test area).
- Instrumentation:
- Use Class 1 sound level meters or equivalent in accordance with IEC 61672‑1 / IEC 61672‑3 (or IEC 60651 where referenced).
- Calibration devices must meet IEC 60942; calibration checked at start and end of runs. Deviations > 0.5 dB invalidate a measurement series.
- Windscreens for microphones as recommended by the mic manufacturer.
- Microphone positions: Two microphones (one per side) located (7.5 ± 0.05) m from the centreline and (1.2 ± 0.02) m above the test surface; no obstructions between source and microphones.
- Environmental measurements:
- Air and surface temperatures measured with instruments accurate to at least ±1 °C; infrared thermometers are not permitted for air temperature.
- Wind, background sound and meteorological conditions must be recorded and meet the standard’s limits.
- Vehicle and tyre preparation: Specification for test vehicle, wheelbase, tyre load, inflation pressure and operating conditions to minimize vehicle influence on results.
- Data processing: Includes temperature correction, normalization to reference speeds and regression-based slope calculations (aligned with UN Regulation 117). The 2019 edition corrected the regression slope formula.
Applications and users
- Tyre manufacturers: product development, acoustic benchmarking and quality control.
- Vehicle OEMs: integration testing and NVH (noise‑vibration‑harshness) assessment.
- Independent test laboratories: certified tyre acoustic testing and reporting.
- Regulators and compliance bodies: supporting conformity checks where coast-by measurements are required.
- R&D teams: investigating tyre-road interaction and noise mitigation strategies.
Related standards
- ISO 10844 - test track specification
- ISO 3833 - vehicle categories
- IEC 61672 series - sound level meters
- IEC 60942 - sound calibrators
- UN Regulation 117 - tyre sound measurement alignment
Using ISO 13325:2019 ensures consistent, reproducible tyre-to-road sound emission data for coast-by tests, supporting product improvement, compliance and comparative acoustic evaluation.
