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.

The Working Party on Noise and Tyres held its eighty-fourth session from 2-4 September 2026 in Geneva. GRBP adopted a draft new Supplement to the 02 series and a draft new Supplement to the 04 series of amendments to UN R117, and agreed to submit these to WP.29 and AC.1 for consideration and vote at their March 2027 sessions. GRBP adopted the content of a proposal for a new supplement to UN R64 and agreed to postpone submission to WP.29 until further notice. GRBP adopted revised Terms of Reference for the IWG on Real Driving-Additional Sound Emission Provisions with extended mandate until February 2028.

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.

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.

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 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.

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.

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.

The Task Force on Tyre Abrasion convened to address strategic and technical aspects of C3 heavy-duty commercial vehicle tyres. Discussion focused on harmonising market segmentation between European long-haul 22.5" tyres and Japanese all-position tyres under the 1958 Agreement, developing parallel indoor drum and on-road convoy test methods with technological neutrality, and addressing infrastructure funding and test method readiness by March 2030 GRBP adoption and June 2030 WP.29 adoption. Additional topics included Standard Reference Test Tyre incompatibility for trailer axles, simulation tools for tyre type extensions, regulatory definition of tyre type, novel hardware concepts, and the exclusion of retreaded tyres from initial UN R186 scope.

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.

Report on the Task Force on Tyre Abrasion’s work from February to October 2026. Foundational methodologies for C1 tyres were adopted and incorporated into a new UN Regulation 186 on tyre abrasion, with a two-stage implementation approach requiring new tyre type approvals from 30 June 2028 and mandatory approval from 30 June 2030, with fitting of pre-June 2030 tyres on vehicles permitted until 30 June 2032, and stage 2 introducing tighter limits with new approvals from 30 June 2033 and mandatory approval from 30 June 2035. C2 test method development is ongoing with an informal document presentation targeting February 2027 submission of a formal working document. For C3 tyres, a brainstorming session was planned for October 2026 in Brussels to develop simplified test methods before physical testing, focusing initially on long-haul and regional 22.5-inch tyres.

Progress report on the Task Force on Tyre Abrasion covering February to October 2026. Work on UN Regulation on tyre abrasion for C1 tyres has concluded, with new UN R186 adopted at WP.29’s 199th session in June 2026, implementing a two-stage approach with initial application from 30 June 2028 and increased stringency from 30 June 2033. C2 test method development is ongoing with formal working document postponed to February 2027; C3 tyre work commenced with brainstorming session in October 2026 targeting working document in February 2027. The Task Force proposes conversion to an Informal Working Group.

Proposal to amend Annex 7, paragraph 2.3.1 to explicitly frame the area of valid values for factor x, requiring that the factor x determined by measurements shall always be at least 0.10 and not exceed the values provided by the parameter table in Appendix 2 to that Annex. The document explains that factor x is used to split constant speed test results energetically into tyre rolling sound and power train mechanic references, and that measurement variations can cause significant variability in calculated values, particularly when factor x exceeds 0.90.

Proposal to amend Annex 7, para. 2.3.1 to constrain the factor x determined by discrete coast-down measurement to a minimum of 10 and a maximum of 90 for internal combustion engine and hybrid electric vehicles, or 95 for electric vehicles, ensuring the Sound Expectation Model remains robust against measurement variations in tyre rolling sound and powertrain mechanic sound splitting.

Considerations by TF-Data Analysis regarding tyre slopes, power train slopes, and part load model for the RD-ASEP Sound Expectation Model. Tyre slopes α = 40 and β = 20 are confirmed as appropriate for UN R117 approved tyres. Power train slopes are confirmed as well-framed to normal vehicle behaviour and consistent with Annex 7 ASEP Slope-Assessment principles. For part load model, the function is confirmed for ICE vehicles and HEV in ICE mode, while for EVs and HEVs in EV mode the part load area may require reworking, but the part load model should be applied uniformly to all vehicle techniques.

Progress Report (February 2026 – September 2026)
Conclusion of work on UN Regulation on tyre abrasion for C1 tyres, launch of C2 work, outlook for C3 work