UN R117 Supplement 2 (03 series) · UNECE Regulation No. 117 (ECE R117) — Uniform provisions concerning the approval of tyres with regard to rolling sound emissions and/or to adhesion on wet surfaces and/or to rolling resistance.
UN R117 — Supplement 2 to the 03 series of amendments
Supplement 1 → 2
- What changed
- Paragraph 2.18. adds the reference tyres “SRTT19.5 siped” and “SRTT22.5 siped”. The wet grip index of class C2 and C3 tyres and the snow grip index in paragraph 4.8.4. now include a factor f.
- As from 7 July 2025, Contracting Parties grant rolling sound type approvals only with the new temperature correction formula of Annex 3, paragraph 4.2.2.
- As from 1 September 2028, Contracting Parties are not obliged to accept certain approvals to this supplement first issued after 31 August 2028. These are approvals with a wet adhesion test in new state (Annex 5) or a snow performance test (Annex 7) using SRTT19.5 or SRTT22.5.
- Why
- The main goal is to improve the reproducibility of the snow grip test method with new siped C3 reference tyres.
- SRTT19.5 and SRTT22.5 were not interchangeable for the wet grip test, which caused uncertainty in testing and logistic difficulties.
- The proposal adds a new temperature correction formula for rolling sound and removes the now obsolete Annex 4.
Q1What changed212 changes
New siped reference tyres and ASTM standard updates (para. 2.18.)
Paragraph 2.18. now also defines “SRTT19.5 siped” (ASTM F3678 – 23, size 245/70R19.5) and “SRTT22.5 siped” (ASTM F3677 – 23, size 315/70R22.5). For SRTT14, SRTT16, SRTT16C, SRTT19.5 and SRTT22.5, the paragraph now refers to newer editions of the ASTM standards. Item (c) for the “moulded SRTT16 worn” now reads “F3611 – 22e1” instead of “F3611-22”. In the ice performance text for class C1 tyres, SRTT16 storage now follows ASTM F2493 – 23, not F2493 – 20.
Snow grip tests with the siped reference tyres (paras. 6.5.1. and 8.3.2.1., Annex 7)
In the table of paragraph 6.5.1., the reference tyres “SRTT19.5, SRTT22.5” now also include “SRTT19.5 siped, SRTT22.5 siped”. The snow grip index in paragraph 4.8.4. now has a factor f. The factor is 1.000 for SRTT19.5 and SRTT22.5, 1.570 for SRTT19.5 siped and 1.680 for SRTT22.5 siped. In paragraph 4.9.2., f also applies to SG1, the comparison between the control tyre and the reference tyre. The test report in Annex 7, Appendix 3, Part 5 has a new row for f. On the tyre manufacturer's request, class C3 verification tests under paragraph 6.5.1. may use the same reference tyre as the original approval (new paragraph 8.3.2.1.).
Wetted track friction for class C2 and C3 tyres (Annex 5, Part (B), para. 1.1.1.)
Under paragraph 1.1.1., the class of the candidate tyre and the method (trailer or vehicle) now decide how the wetted track friction is established. Before, this was at the discretion of the Contracting Party. A new table gives the friction range for each tyre class and reference tyre, for the trailer method (μpeak) and the vehicle method (BFC). New paragraph 1.1.1.2. adds a method using SRTT16C, SRTT19.5, SRTT22.5, SRTT19.5 siped and SRTT22.5 siped, with no temperature correction. In paragraphs 2.1.2.13. and 2.2.2.7.2., new item (b) requires the initial and final reference tyre averages of a test cycle within the paragraph 1.1.1. range. Paragraph 1.1.2. is deleted; it required the Type Approval Authority to satisfy itself of the track characteristics from test report evidence.
Wet grip index of class C2 and C3 tyres (Annex 5, Part (B), paras. 1.4., 2.1.2.14., 2.2.2.4. and 2.2.2.7.5.)
Paragraph 1.4. now lists SRTT19.5, SRTT22.5, SRTT19.5 siped or SRTT22.5 siped for class C3 tyres. Before, it split class C3 tyres into a “Narrow family” (SNominal < 285 mm) and a “Wide family” (SNominal ≥ 285 mm). The wet grip index formulas in paragraphs 2.1.2.14. and 2.2.2.7.5. now include a correction factor f that depends on the SRTT used. Factor f is 1 for SRTT16C (class C2) and for SRTT19.5 and SRTT22.5 (class C3), and 1.02 for SRTT19.5 siped and SRTT22.5 siped. In paragraph 2.2.2.4., the load range of 60 per cent to 100 per cent now applies to the SRTT and the candidate tyre's load capacity. The load is now expressed as a percent of the nominal static load and rounded to the nearest integer.
Rolling sound temperature correction and Annex 4 (paras. 8.3.4. and 12.12. to 12.14., Annex 3, paras. 4.2.1. and 4.2.2.)
New paragraph 4.2.2. gives a new temperature correction formula for rolling sound levels of class C1 and class C2 tyres (ϑref = 20 °C). Paragraph 4.2.1. applies until 6 July 2025 (paragraph 12.12.), and paragraph 4.2.2. from 7 July 2025 (paragraph 12.13.). Under paragraph 12.14., Contracting Parties continue to grant extensions of approvals first granted before 7 July 2025 with paragraph 4.2.1. A new test on a different representative tyre size for an extension after 6 July 2025 must use paragraph 4.2.2. New paragraph 8.3.4.: on the tyre manufacturer's request, verification tests for paragraph 6.1. approvals may use the same temperature correction formula as the original approval. Annex 4 “Specifications for the test site” is now “Reserved”, and the test site text no longer refers to Annex 4.
Transitional provisions for the C3 reference tyres (paras. 12.15. to 12.20.)
Under paragraphs 12.15. and 12.16., as from 1 September 2028, Contracting Parties are not obliged to accept certain approvals first issued after 31 August 2028. These are approvals to this supplement with Annex 5 wet adhesion tests in new state or Annex 7 snow performance tests using SRTT19.5 or SRTT22.5. Under paragraphs 12.17. and 12.18., Contracting Parties continue to grant extensions of class C3 approvals first granted before 1 September 2028 with SRTT19.5 or SRTT22.5. If an extension after 1 September 2028 needs a new test on a different representative tyre size, SRTT19.5 siped or SRTT22.5 siped will be used. Paragraph 12.20. names reference tyres for the wet adhesion track characteristics from 1 September 2028: SRTT16C (class C2), SRTT19.5 siped or SRTT22.5 siped (class C3). Contracting Parties are not obliged to accept approvals to this supplement if the track characteristics are not established with these tyres.
Snow tyre definition, title of paragraph 6. and editorial updates (paras. 2.13. and 6.)
In the “Snow tyre” definition of paragraph 2.13., “structure” is now “construction”, and “in snow conditions” is now “in mud and/or snow conditions”. The tyre's ability to “initiate or maintain” vehicle motion is now its ability to “initiate and control” vehicle motion. The title of paragraph 6. is now “Requirements” instead of “Specifications”. Paragraph 8.3.2., Annex 7, paragraph 2. and Annex 8, paragraph 2.4.5.1.2. now refer to paragraph 6.5. or 6.5.2. instead of 6.4. or 6.4.2. References to ISO standards are updated, and the unit is now written “newtons” instead of “newton”. In Annex 9, the definitions of “Central zone” and “Mould parting line” now refer to Figure 4 and Figure 1.
Q2Why it changed
- Proposed by
- Experts from the European Tyre and Rim Technical Organization
- Working party
- GRBP, 79th session (February 2024)
Reasons
The main goal is to improve the reproducibility of the snow grip test method. To do this, the proposal replaces the current C3 reference tyres SRTT19.5 and SRTT22.5 with new siped versions. These tyres will also be used for the wet adhesion test. So the wet grip procedure for class C2 and C3 tyres in Annex 5, Part (B) needs changes.
Sources (2)
“the main goal of this supplement is to improve the reproducibility of the snow grip test method by replacing the current reference tyres C3 SRTTs 19.5 and 22.5 with the new reference tyres C3 SRTTs 19.5 and 22.5 siped.”
“As these new reference tyres will be also used to assess the wet adhesion performance, adaptations are needed for the C2 and C3 class tyres wet grip index procedure in Annex 5 - Part (B).”
For the wet grip test, SRTT19.5 and SRTT22.5 were not interchangeable, because their choice depended on the section width of the candidate tyre. This caused uncertainty in testing and logistic difficulties. The proposal removes this constraint. The method to check the wet friction of the C2 and C3 track used the C1 SRTT16 µ-peak. The proposal calls this method complex and not really effective. It therefore validates the track and the test results of each session with the same method and reference tyres as the test.
Sources (5)
“SRTTs 19.5 and 22.5 are currently not interchangeable for the wet grip index test, being their choice linked to the section width of the candidate tyre.”
“This provision generates uncertainty in testing and logistic difficulties, being not always possible to fit SRTT and the candidate tyre under the same vehicle.”
“It is then proposed to eliminate the existing unnecessary constrain.”
“the method to measure and validate the wetted frictional properties of the C2 and C3 track surface is based on the C1 SRTT16 µ-peak. This provision is complex and not really effective”
“it is proposed to validate both the C2 and C3 track surface and the tests results of each test session using the same method and the same reference tyres used in the evaluation program itself.”
The transitional provisions let technical services adapt the test tracks to the new requirements, if needed. They also assure a smooth transition to the new siped SRTT19.5 and SRTT22.5 without premature disposal of the current SRTT19.5 and SRTT22.5.
Sources (2)
“Transitional provisions are introduced to ensure that technical services may adapt, if needed, the test tracks to the new requirements”
“to assure a smooth transition to the new SRTTs 19.5 and 22.5 siped without premature disposal of current SRTTs 19.5 and 22.5.”
In line with an amendment for Supplement 2 to the 04 series, the proposal adds a new temperature correction formula for rolling sound emissions. The formula covers tyres of classes C1 and C2. The proposal also removes the content of Annex 4, which is now obsolete, and all references to it.
Sources (2)
“In line with the amendment adopted at the seventy-eighth session of the Working Party on Noise and Tyres (GRBP) for Supplement 2 to the 04 series of amendments to UN Regulation No. 117”
“we propose to introduce a new temperature correction formula for the rolling sound emissions of tyres of classes C1 and C2 and to remove the content of the now obsolete Annex 4 as well as all its references.”
Proposer's reason (informal document GRBP-79-22)
For the snow grip test, the proposer compared four scenarios for the correlation factors of the new siped C3 reference tyres. It proposed two different factors: f = 1.57 for SRTT19.5 siped and f = 1.68 for SRTT22.5 siped. The proposer says none of the scenarios is self-consistent, but this one at least keeps unchanged the current situation for the measured snow grip index. The proposer presents it as a compromise intermediate solution.
Submitted by Experts of the European Tyre and Rim Technical Organisation. Working party adoption: ECE/TRANS/WP.29/GRBP/77, para. 23.
Sources (7)
“12. Regarding the snow grip test procedure, as requested by GRBP Chairman during the 78th session, ETRTO contacted JAPAN.”
“As the passage between the results obtained with the new siped SRTTs and the current SRTTs is provided by the correlation factor, four different scenarios can be considered.”
“to introduce two different correlation factors for the snow grip testing of C3 tyres in the case the new C3 siped SRTT’s are used:”
“f = 1.57 for SRTT19.5 siped”
“f = 1.68 for SRTT22.5 siped”
“Although none of the illustrated scenarios is self-consistent, scenario 4 at least keeps unchanged the current situation for the measured snow grip index.”
“It is presented as a compromise intermediate solution aimed primarily to improve the reproducibility of the snow grip test method.”
Document trail
- 2023-11ProposalECE/TRANS/WP.29/GRBP/2024/9ETRTO proposal for Supplement 2 to the 03 series
- 2023-11ProposalECE/TRANS/WP.29/GRBP/2024/12ETRTO proposal with the new temperature correction and editorial changes
- —Amended in sessionGRBP-79-22ETRTO amendments to ECE/TRANS/WP.29/GRBP/2024/9
- —Amended in sessionGRBP-79-49Amendments by France to ECE/TRANS/WP.29/GRBP/2024/12
- —Working party adoptsECE/TRANS/WP.29/GRBP/77GRBP session report, para. 23
- 2024-04Sent to WP.29ECE/TRANS/WP.29/2024/72Text that GRBP sent to WP.29 and AC.1
- 2024-06WP.29 adoptsECE/TRANS/WP.29/1179Adopted at the 193rd session (session report, para. 162)
- 2025-01-10In forceC.N.58.2025.TREATIES-XI.B.16.117UN depositary notification
Q3Who is affected
Vehicle manufacturer
- No direct action for this role.
Component supplier
- For approvals first issued after 31 August 2028, plan Annex 5 and Annex 7 tests without SRTT19.5 or SRTT22.5.
- Check C1 and C2 rolling sound levels with the Annex 3, paragraph 4.2.2. correction for approvals from 7 July 2025.
- Under paragraph 8.3.2.1., decide whether to request the original reference tyre for paragraph 6.5.1. verification tests of class C3 tyres.
- Under paragraph 8.3.4., decide whether to request the original temperature correction formula for paragraph 6.1. verification tests.
- Check that your snow tyres meet the changed “Snow tyre” definition in paragraph 2.13.
Technical service / Approval authority
- Check C2 and C3 wetted track friction against the range for the SRTT and method in the paragraph 1.1.1. table.
- Repeat the complete test cycle if the initial or final reference tyre average is outside the paragraph 1.1.1. range.
- For class C3 tyres tested against SRTT19.5 siped or SRTT22.5 siped, use f = 1.02 in the wet grip index.
- For snow grip tests against SRTT19.5 siped or SRTT22.5 siped, use f = 1.570 or f = 1.680 respectively.
- For type approvals from 7 July 2025, apply the Annex 3, paragraph 4.2.2. temperature correction to C1 and C2 tyres.
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ⓘ This report gives advice only. It is not legal or type-approval advice.