Proposal to solve the discrepancies between the test report format and the description of the test method for C2 and C3 tyres.

Proposal replaces the GRBP2026/26

Road legal race tyres are currently defined in the new UN R186 on abrasion but fall out of its scope. Considering that the new UN R186 on abrasion applies only to tyres that conform to UN Regulation No. 117., it is proposed to replicate therein the definition, the marking and the requirements of road legal race tyres by adding the new paragraphs 2.21., 4.5. and 6.9.

The agenda includes welcome and opening remarks, introduction of participants and organizations, adoption of the draft agenda, review of minutes from the 13th session of June 2026, review of Terms of Reference from GRBP 78th Session (GRBP-78-13), UN R51 matters, review of report to GRBP, and determination of the date and place of the next meeting, scheduled for 20–22 October in Barcelona, Spain.

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

RD-ASEP includes technical background and vehicle application guidance for Real Driving Additional Sound Emission Provisions under UN R51.03 Supplement 7 Annex 9 for the mandatory monitoring phase between 07/2023 and 06/2024. RD-ASEP, referenced in GRB-68-03, applies to vehicles of category M₁ and N₁ equipped with internal combustion engines and covers engine speeds up to 95% of typical driving in speed ranges applicable to sub-urban conditions. A Sound Expectation Model predicts vehicle sound levels at randomly selected operation conditions by splitting measured pass-by test results into tyre rolling sound, mechanical no-load sound, and dynamic sound components, using reference values from Annex 3 type approval tests with logarithmic functions and parameter table slopes. Compliance assessment allows measured sound to exceed calculated expected sound by not more than 2 dB for maximum two test runs out of fifteen. Model validation with 2024 monitoring database confirms the tyre rolling sound and power train sound models represent well approved tyres and engines, with less than 5 dB typically separating pass-by run results from the limit.

An improvement intended to increase vehicle robustness in Annex 3 creates more difficulties in RD-ASEP assessment. Small variations in Annex 3 parameters may result in unexpected substantial exceedances in Annex 7. Minimal changes in the calculated tyre share at the anchor point may cause vehicles to fail Annex 7. The regulation should ensure realistic test effort and workload for compliance verification, as current requirements may require up to 180 combinations per type across test tracks, temperatures, driving modes, and tyres.

The IWG RD-ASEP is developing a mandatory test procedure to assess compliance with paragraph 6.2.3 of UN R51.04, ensuring vehicle noise emissions at various speed, load, and acceleration conditions are linked to vehicle physics without defeat devices. R51.04 RD-ASEP expands testing from full acceleration only to any acceleration position, increases vehicle speed range from 20–80 km/h to 1–100 km/h, adds vehicle performance criteria, requires random test points for approval rather than manufacturer declaration, and can test gears and loads previously unavailable. An updated GRB-68-03 will accompany R51.04. Submission targets include informal draft September 2026 and expected working document adoption February 2028, with TOR extension requested through 2028.

Proposal to amend para. 6.2.1.1. to permit testing of vehicle sound either indoors or outdoors with equivalent results, add new Annex 11 specifying indoor testing provisions, amend Annex 1 to insert para. 8.5. and 8.5.1. requiring documentation of test method selected, amend Annex 3 para. 1. to specify sound level meter requirements for indoor testing per IEC 651 and IEC 61672-3, amend Annex 3 para. 1.1.1. to provide calibration procedures for indoor testing per IEC 942:1988, amend Annex 3 para. 1.3. to exempt wind speed monitoring for indoor facilities, amend Annex 3 para. 2.1. and add para. 2.1.4. to specify outdoor and indoor test site requirements per ISO 362-3:2022 and ISO 26101, add para. 2.1.5. specifying indoor ambient conditions, add para. 2.2.7. addressing test mass for indoor dynamometer testing, amend Annex 3 para. 3. to specify outdoor and indoor test procedures per ISO 362-3:2022 Variant A, amend Annex 3 para. 3.1.1. to clarify outdoor testing microphone placement, add para. 3.1.1.4. defining virtual lines and simulated vehicle speeds for indoor testing, and renumber former paras. 3.1.1.4. and 3.1.1.5. as 3.1.1.5. and 3.1.1.6.

Rationale for Figure Part B.5 of GRBP-84-36-Rev.1

The 15th RD-ASEP informal group session will be held at Nissan Technical Center Europe Spain in Barcelona. The venue is located 11 minutes walk from Mercabarna Metro Station Line 9S. Participants should make hotel reservations independently; options include areas near metro line L9S or city center near metro line L5, which connects with L9S. Participants must provide last name, first name, phone number, company name, and email in advance.

The agenda includes a review of Terms of Reference from GRBP 78th Session (GRBP-78-13), report of Data Analysis Task Force, review of issues list, review of draft text, and discussion of UN R51 matters. Dates and locations of 2027 meetings will be determined.

The Task Force Data Analysis meeting scheduled for 15 September 2026 will discuss database pilot documents covering amendments to factor x, reference acceleration, AVAS term considerations, simplified EV models, and RD-ASEP model slopes. The task force will prepare proposals based on draft UN R51.04 for items 13–19 from the Editing TF issues list and address a question regarding the phrase “but no more than 2.0 m/s” in paragraph 3.1.2.1.4.3 concerning acceleration values for vehicles with single gear ratios.

Document presents considerations on factor x used in the Sound Expectation Model to split constant speed test results into tyre rolling sound and power train mechanic references. Factor x values are concentrated between 80 and 99, indicating tyre dominance. Small variations in measurements cause disproportional variability in the minor sound source when one source dominates. Two options are proposed: Option 1 requires factor x determined during type approval to be reported and used for subsequent assessments, with any redetermination not exceeding the type approval value; Option 2 requires the power train reference from type approval to be used for all further assessments regardless of measurement variations.

Proposal to amend the determination of reference acceleration aREF by introducing a theoretical calculation formula based on PMR, rated engine speed S, and vehicle mass mro, with a correction function accounting for transmission losses, virtual mass increase, tyre slip, and turbo delay, and to allow manufacturers to alternatively determine reference acceleration by discrete measurements.

Document presents considerations on revising the AVAS term in the RD-ASEP Sound Expectation Model to align with UN R138.02 specifications for electric and hybrid electric vehicles. Two options are discussed: Option 1 implements only constant speed specifications from UN R138.02, while Option 2 extends this with an additional term to reflect interpretation of paragraph 6.2.8 for accelerated conditions. A revised AVAS term formula applicable for vehicle speeds up to 50 km/h is proposed.

Document presents considerations on amendments to the RD-ASEP Sound Expectation Model SEM. A simplified approach for electric vehicles is proposed based on Supplement 11 to UN R51.03, using a tyre rolling sound curve with slopes identical to internal combustion engine and hybrid electric vehicles, plus an acceleration term from UN R51.03 Supplement 11 as an additional term, and the AVAS term from Option 1, without other parts of the SEM.

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.

Document presents suggested revisions to test procedures in Annex 7 and Annex 7 Appendix 1:

• Renumber para. 4.4. into paras. 4.4.1. through 4.4.8. to structure target operation conditions,
• Insert new para. 4.4.7. to permit acceptance of measurement runs outside the control range when agreed by manufacturer and authority,
• Modify para. 3.6.1.1. to define maximum reference acceleration for a selected reference v-t-e ratio and clarify determination procedures,
• Add provision that in case calculated acceleration is negative, the value is set to zero,
• Restructure para. 2.2.1.2. to introduce subsections 2.2.1.2.1. and 2.2.1.2.2. for parameters from acceleration and constant speed tests respectively, and modify parameter definitions including use of vPP,CRS instead of fixed 50 km/h reference speed.