The secretary reported on C1 tyre testing activities. The Netherlands and Germany noted potential delays in Normal tyre testing at high temperature by end of March due to temperature conditions. The co-chair presented a status report for GRBP’s 83rd session, which the group approved. Future meetings are scheduled for February through April.

The 73rd session of the Informal Working Group on Wet Grip of Worn Tyres convened remotely on 31 March 2026. The agenda and previous session minutes from 3 February 2026 were adopted. The WTPP secretary reported on testing activities status for the workplan stage 1 for C₁ tyres, with results to be presented to GRBP at its 84th session in September 2026. ETRTO stated conclusions can only be made on complete datasets. Future meetings are scheduled through July 2026.

The agenda for the 74th session of the Informal Working Group on Wet Grip of Worn Tyres scheduled for May 19th, 2026, remotely via Teams. The agenda includes welcome and opening remarks, adoption of the agenda and minutes of the previous 73rd session meeting held 31 March 2026, discussion of the workplan 2025 for C1 tyres status test campaign, and determination of the next meeting date.

The Worn Tyres Post-Processing task force held its 34th session on 13 May 2026. Ninety-three percent of 3PMSF tests have been completed and members agreed to start the post-processing activity for the 3PMSF cluster. Test results for Normal tyres will be delivered once the high temperature range will be achieved. Future sessions are scheduled for 28 May, 15 June, 2 July, and 15 July 2026.

Draft minutes of the 74th session of the Informal Working Group WGWT held May 19th, 2026 (9:00–10:00 CET), remotely. Attendance per document WT-74-04. Agenda adopted. Previous meeting minutes of 73rd session (31 March 2026) not uploaded; to be adopted at next session per document WT-74-01. WTPP secretary updated on testing activities status per document WT-74-02. 3PMSF data from one test center pending before sharing anonymised data to WTPP for analysis. JASIC provided completed test data on 3PMSF and Normal tyres. Next meetings: WTPP 35 (28 May 09:00–10:30 CET); WTPP 36 (15 June 09:00–10:30 CET); 75th session (16 June 8:00–9:00 CET); WTPP 37 (02 July 09:00–10:30 CET); WTPP 38 (15 July 09:00–10:30 CET) per document WT-74-02.

The agenda includes discussion of the workplan 2025–2026 for C1 tyres and test campaign status, preparation of the IWG WGWT status report to GRBP 84th session (September 2026), and identification of next meetings scheduled for 2 July and 15 July 2026.

WTPP has started post-processing activity for the 3PMSF cluster. 90% of test results for normal tyres are expected to be reached by June 2026. WTPP members are working on dataset correction including typos and rounding, and definition of the outliers.

Minutes of the 75th session of the Informal Working Group WGWT held 16 June 2026 on-line. The agenda was adopted. Previous meeting minutes from the 73rd session (31 March 2026) and 74th session (19 May 2026) were adopted. WTPP secretary updated on testing activities status per document WT-75-2. ETRTO stated the agreed number of tests was a statistical minimum and IWG WGWT conclusions to GRBP must be based on complete test results. IWG WGWT agreed to await WTPP conclusions on outliers before deciding whether to keep the current number of tests or make additional tests. The co-chair stated a status report must be prepared for GRBP 84th session (September 2026) and suggested an IWG WGWT meeting days before GRBP. Next IWG WGWT meeting scheduled for 28 August 9:00–10:00 CET.

Draft agenda of the 76th session of the Informal Working Group WGWT scheduled for August 28th, 2026 on-line. The agenda includes welcome and opening remarks, adoption of the agenda, adoption of the minutes of the 75th session of 16 June 2026, review of work plan 2025-2026 for C1 tyres, review of IWG WGWT status report for GRBP 84th session of September 2026, and next meetings.

The Worn Tyres Post-Processing task force completed data collection for 3PMSF and Normal tyres, each with 57 samples representing 100% of target. Ongoing activities include outliers analysis of the 3PMSF and Normal cluster and post processing of the data conclusions.

The IWG for Wet Grip on Worn Tyres reports progress on evaluating methods for preparing tyres of Class C1 to be tested in worn state at type-approval, defining test conditions and methods, establishing type-approval thresholds for wet grip performance, and addressing requirements for classes C2 and C3. Test Campaign Stage 1 assesses test procedure precision per GRBP-80-11, with normal and 3PMSF tyres completely tested at 13 test centres. Outliers analysis and KPI target confirmation are ongoing. Stage 2, if needed, is planned for 2026-2027.

The 76th session of the Informal Working Group on Wet Grip of Worn Tyres convened on 28 August 2026 remotely. The agenda was adopted and previous meeting minutes from the 75th session were adopted. The WTPP secretary updated the IWG WGWT on testing activities status; the Co-chair noted the Gantt should reflect additional postprocessing time extending to September 2026. The Co-chair presented the status report for GRBP 84th session, with an ETRTO expert proposing clarification of the word outlier. A revised status report will be sent to GRBP secretariat. Next meetings are scheduled for 11 August, 14 September, and 28 October 2026.

Draft agenda for the 77th session of the Informal Working Group on Wet Grip of Worn Tyres, scheduled for October 28th 2026, remotely. The session will cover welcome and opening remarks, adoption of the agenda, adoption of minutes from the 76th session held on 28 August 2026, the workplan 2025-2026 for C1 tyres and outcome from WTPP, and discussion of next meetings.

WTPP has completed data collection and shared results with members. All tests have been completed. The post processing activity is ongoing, with exclusion of non-compliant data points. Assessment of test method precision improvement is underway.

Presentation on Stage 1 test campaign results for WGWT test procedure precision. ETRTO achieved a Weighted Standard Deviation of 0.071 for Normal and 3PMSF categories, exceeding the 12% targeted KPI improvement by over 50%, demonstrating that R117 amendments to improve precision were effective. ETRTO states the KPI target is fully achieved and is not in favor of JASIC’s proposal to revise correction formula coefficients, as the 2025 dataset is not representative and such revision would deteriorate standard deviation of the 2021 Round Robin Test dataset.

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.

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.