Proposal to amend para. 2.18. to update Standard Reference Test Tyre definitions with ASTM International standards E1136 19, F2493 24, F2872 25, F2871 25, F2870 23, F3678 25, and F3677 23 for specified tyre sizes and designations, and amend para. 12.21. to permit Contracting Parties to continue accepting existing type approval and extensions to existing type approvals of class C3 tyres first granted before 1 September 2028 using SRTT19.5 or SRTT22.5, with SRTT19.5 siped or SRTT22.5 siped required for new tests performed on different representative tyre sizes for extensions granted after 01 September 2028.