Overview
ISO 15222:2021 - "Truck and bus tyres - Method for measuring relative wet grip performance - Loaded new tyres" specifies a standardized test method to measure the relative wet grip braking performance of new commercial vehicle tyres under loaded conditions on a wet-paved surface. The standard defines test methods intended to reduce variability by requiring the use of a reference tyre (standard reference test tyre, SRTT) and detailed procedures for track, atmospheric and tyre preparation. It applies to all truck and bus tyres used on commercial vehicles, excluding studded tyres and professional off‑road tyres.
Key topics and technical requirements
- Test methods: Two primary approaches are described - the vehicle method (tyre set mounted on a standard vehicle) and a trailer / tyre test vehicle method (instrumented trailer or special tyre test vehicle).
- Reference and control tyres: Use of a reference tyre (R) and, where needed, a control tyre (C) to limit variability and enable comparison of a candidate tyre (T).
- Measured metrics: Definitions and measurement of the braking force coefficient (BFC), dynamic tyre braking force coefficient (µ(t)), and peak braking force coefficient (µ_peak), plus procedures to detect wheel lockup and measure vertical load.
- Test conditions: Requirements for track characteristics, wetting conditions, atmospheric conditions, tyre load and inflation, tyre preparation and break-in, and instrumentation for real-time force measurement.
- Data processing and validation: Prescribed calculations for adjusted braking coefficients, validation of runs and cycles, and computation of a relative wet grip index referenced to the SRTT.
- Variability control: Rules for SRTT selection (noting the change from SRTT 14" to SRTT 16"), storage of control tyres, and replacement criteria to maintain consistency across tests.
Practical applications and intended users
ISO 15222:2021 is used for:
- Tyre manufacturers: R&D, product development, and comparative performance evaluation between product lines.
- Independent test laboratories: Reproducible wet grip testing for certification, quality control and supplier verification.
- Regulatory and standards bodies: Harmonized methods to support safety regulations or labelling schemes for truck and bus tyres.
- Fleet operators and procurement teams: Objective wet grip performance data to inform tyre selection for safety and braking performance in wet conditions.
Related standards and references
Key normative references include ISO 23671 (passenger car wet grip method alignment), ISO 4209-1, ISO 4223-1, and ASTM E965-15 (pavement macrotexture). These linked standards support terminology, tyre/rim specifications and track surface measurement methods.
Keywords: ISO 15222:2021, truck and bus tyres, wet grip, relative wet grip, braking performance, standard reference test tyre, SRTT, tyre test vehicle, braking force coefficient.