Draft minutes of the 77th session of the Informal Working Group on Wet Grip of Worn Tyres held on 28 October 2026. The group reviewed and discussed preliminary conclusions from data analysis on test precision for worn tyre wet grip testing, including comments from JASIC and ETRTO. Discussion covered whether the obtained dispersion level of 0.071 is sufficient, the appropriateness of test campaign methodology, and the feasibility of achieving precision levels comparable to new tyre wet grip testing given the intrinsic variability from candidate tyre buffing and aquaplaning effects.

JASIC presents Stage 1 findings on worn tyre wet performance testing precision improvement. JASIC proposes that the KPI target should be the same weighted value as wet grip for new tyres (100% improvement), compared to ETRTO’s 50% improvement target. Stage 1 weighted analysis results show 50% improvement, or 100% improvement if coefficients of the GB formula are revised. The 2019-21 dataset is outside Stage 1 assessment scope due to unmet prerequisites such as buffed SRTT tyre application and reduced sample sizes. JASIC proposes revising GB calculation formula coefficients for the trailer method based on Stage 1 data, with continuous investigation to follow.

Test precision weighted analysis to exclude NOK data from the worn tyre wet performance test. Analysis of precision using dataset without NOK data shows the same trend as analysis based on full dataset. New coefficients for the GB formula significantly improve precision, which is now comparable to new tyre wet grip test. Strong correlation exists between current and new formulas, making it possible to continue current worn-tyre wet grip criteria. JATMA proposes to revise coefficients of the GB calculation formula based on Stage 1 data.

JASIC submits comments on ETRTO analysis results for the worn tyre wet performance test precision improvement study. JASIC argues that 2019-2021 test campaign data is not acceptable for Stage 1 analysis because it used buffed SRTT rather than the molded SRTT prerequisite, original sample sizes of n=4 per SKU were reduced to n=2 or n=1 after excluding NOK data rendering statistical analysis unreliable, and the data falls outside Stage 1 assessment scope. JASIC recommends not using 2019-2021 data for weighted assessment, proposes defining M+S tyre coefficients by averaging 3PMSF and NORMAL coefficients, and recommends revising GB calculation formula coefficients for trailer method based on Stage 1 data.