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Description
Within the framework of working group ISO/TC43/SC1/WG33, which is dealing with measuring methods for comparing traffic noise on different road surfaces, the revision of ISO/TS 11819-3 is ongoing since 2025. This technical specification concerns reference tyres used in CPX (Close-Proximity) noise measurements. One of the remarks received during the systematic review of this technical specification was to improve the procedure to measure rubber hardness of the reference tyres, which is used as correction factor for the measured sound pressure levels No distinction is currently made between digital and analogue durometers, although some users report different results depending on the device used. A measurement plan for a round robin test was set up where various institutes were requested to repeat measurements on their own P1 tyre by varying only one of the following parameters: durometer type, time setting after contact (for digital durometers), operator (including their level of expertise), measurement day. Participants were asked to measure more points around the tyre and to report all their results, including values that would be discarded according to the current procedure. A substantial dataset from seven institutes was obtained and analysed. Based on this analysis, a proposal for improving the measurement procedure has been put forward. It was determined that the operator’s level of expertise and the device settings are significant parameters. The results will be used as input for the revision of the Technical Specification with the aim of reducing variability and increasing reproducibility of the CPX reference tyre hardness measurements.