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3 rd session of the GRBP Informal Working Group

on Wet Grip on Worn Tyres (WGWT), September 10 th - 11 th (am) 2019




World Forum for Harmonization of Vehicle Regulations (WP.29)

Working Party on Noise and Tyres (GRBP)

Working Group on Wet Grip on Worn Tyres (WGWT), September 10th - 11th (am) 2019


Minutes of the 3 rd session of the Informal Working Group WGWT

September 10 th (9:00- 17:30) - 11 th 2019 (9.00-12.30) CET

At the Palais des Nations, Room XV, Geneva




Working Documents


Welcome and opening remarks

EC that chaired the meeting in their capacity of the IWG Vice-Chair, with Chair (FR) attending through remote connection, welcomed the participants and invited them to a round table introduction.



Introduction of participants and organizations



Adoption of the agenda and the minutes of previous meeting


Agenda has been adopted with the addition of:

-           Request of Germany: validating the buffed tread profile by the Technical Service ahead of the Type Approval test (measuring procedure and method / apparatus) under agenda item 7.

-           Request from EC: Extension to scope of ToR to C2 and C3 under item 10


Minutes of last meeting were approved .



Objective of the meeting


Objective of the meeting was reminded by the chair


-           To finalise the definition of the worn tyre

-           To further work on the workplan

-           To prepare the presentation on the status report to the 70 th GRBP






Action item WT-02-03

ETRTO will share the draft Excel workplan (Step 1) proposal
IWG members are invited to assess the draft proposal and to provide comments for September meeting.


ETRTO proposal (WT-03-07) and France proposal (WT-03-08) were assessed in the IWG.


Action item WT-02-04

ETRTO is requested to provide by next IWG meeting a detailed workplan including a time table.


Action items are replaced by


Action item WT-03-01

ETRTO will prepare detailed workplan considering the requested timing and resources.

Target to deliver workplan proposal: Mid October 2019.


IWG chair asked the different testing facilities whether they intend to participate in the workplan and to which extent they can contribute in the workplan implementation to help to reduce the testing time.


Action item WT-02-05

IWG members that are candidate to perform tests or to provide are asked to inform the IWG by next meeting in September.


Action item is still open.


Action WT-01-11

France will provide more details on the test performed and presented

IWG experts will give their technical feedback and/or opposable/additional tests.


Document WT-03-02 and WT-03-05 are presenting the test campaign status ongoing in France.


France explained the approach to of the study, to measure the Wet Grip performance decrease with wear. IWG appreciated the work and suggested to continue the study up to 2mm worn state. The natural 2mm worn state tyre is suggested to be compared with artificial 2mm worn tyre based on the preliminary draft procedure.


Action item is closed.


The document is also presenting the UN regulatory timeline proposed by France and the GSR timeline.



Industry raised the fact that the very short timeline will have an impact on new tyre development.

Industry needs enough visibility on future specifications (as new tyre design may need from 4 to 8 years development time).


OICA informed that the vehicle Type approval can also be impacted.


IWG agreed that the workplan shall first validate the test methodology, and in a second step to see the absolute necessary specifications (requirements/thresholds) needed for C1.



WT-02-02 rev2














Definition of worn tyre


  1. Tread depth


Action item WT01-01

IWG agreed to the requirements (to be included in the standard) on 4 points in the circumference:

-           Individual tread-depth: 2,0 +/- 0,4mm

-           Average tread-depth in principal groove: 2,0 +/- 0,3mm

-           Average tread-depth total measurements: 2,0 +/- 0,2 mm


Action item is closed.


Action item WT01-02

IWG experts will make the assessment on the buffing tolerance of their buffing equipment. Buffing target is 2 mm for this study (determination of α based on the proposal above).


Document WT-03-03 is the China contribution with the assessment on the buffing procedure and tolerances.

Action item is still open as additional feedback is welcome from the other IWG participants.


  1. Wear profile


  1. Principal grooves

Flat profile (scenario 1 = worst case, to be further assess) and Offset (scenario 2) of the new profile.


Action item WT-02-01

IWG will reflect internally on the scenario 1 and 2 on what need to be considered or assessed in order to have an agreement during September session.


Action item is overdue as document WT-03-04 describes the buffing method proposal.


  1. Shoulder area

IWG agreed on the concept proposed in slide 9 of document WT-02-02-rev2


Action item WT-02-01

Industry is requested to finalize the shoulder wear profile definition. The proposal shall include a specific definition e.g. a k-factor table for the connection point”. Deadline: September


Tyre industry preliminary proposal on worn tyre definition was presented with document WT-03-04


IWG agreed with the Worn Tyre definition proposal as presented (WT-03-04 ) with the following comments:

-           the location of Li and Le need to be considered in the type approval report for ensuring the same test conditions in market surveillance procedure.

-           How to manage the cases of tyres without mould parting line. ( Tyre Industry to investigate internally).

-           The feasibility of the average roughness of 20 μ m shall be confirmed during the test campaign. To verify in the test program whether it is needed to measure the roughness of all test tyres.

-           The procedure shall mention that the roughness measurement shall not be taken in a groove.

-           Check ISO 4287/1997 reference for the surface roughness measurement.

-           To base the test procedure on the ISO test procedure, and to adapt it so as to be feasible for tyres.

-           To prepare a test report template (annex).


The definition of worn tyre as proposed shall be confirmed in the test campaign.


  1. Ageing


Action item WT-01-05

France will provide national data on the medium vehicle mileage per year.

OICA will try to have a more global data.


OICA shared the information from Sectoral Profile – Transport (document WT-03-06) presenting the average mileage/year in Europe. (see table hereunder)



USA informed the IWG that preliminary data shows that the average mileage/year in US is 21561 km/year.

France informed the IWG that the average mileage/year in France is 15452 km/year on 1.700.000 M1 vehicles.


Action item WT-03-02

In order to complete the average mileage/year, China will check whether similar information of average mileage can be shared with the IWG.


Action item WT-03-03

Tyre industry will investigate whether publications are available on the average mileage/tyre, or if a different way to estimate the average mileage of tyres is existing.


Action item WT-03-04

USTMA will provide information on the average demounting tyre age in US.


IWG agreed that the workplan will consider candidate natural worn tyres with an age of about 3 to 4 years (subject to the availability of the tyres) to be compared to artificial worn tyres to evaluate the ageing effect on the wet grip test.

The age of the natural worn candidates shall be recorded.


Action item WT-01-06

Tyre industry will investigate what could be the criteria to define the medium ageing of tyres (needs the outcome of action item WT-01-05)


Action item WT-01-07

EC will provide more information with already existing information: use, recommendation…


EC informed the IWG that they have no information to provide at this moment.


  1. Buffing Roughness definition


Action item WT-01-08

The buffing roughness is less significant but can be kept in the workplan.


Document WT-03-04 is proposing a buffing roughness of 20 µm.

IWG agreed that the test campaign will confirm the roughness of the buffed tyre.


WT-02-02 rev2



Tyre preparation (buffing method)


Action item WT-03-05

ETRTO will present this draft procedure to prepare a worn tyre for September meeting.


-           validating the buffed tread profile by the Technical Service ahead of the Type Approval test (measuring procedure and method / apparatus).


See agenda item 6 and document WT-03-04


Action item is completed





Testing condition


Action item WT-03-06

ETRTO will share the logic and principles of the new wet grip procedure (revised ISO test method) to the IWG.


Presentation was made by ETRTO as per document GRBP-70-20


Action item can be closed  




Follow up of work 

-           Key elements / Planning

-           Measurement campaigns


WT-02-02 rev2


Any Other Business

-           Agenda for next meetings

Target of next meeting is finalising the test campaign workplan.


-           Proposal from Russian Federation

WT-01-01 was considered during the IWG meeting:

Item 1.1: Test method using new or worn SRTT: will be discussed/evaluated during workplan

Item 1.2: worn conditions of candidate tyre: item has been covered

Item 2: Wet grip indices, covered by presentation of France. Subject to be considered by the IWG

Item 3: administrative provisions to be considered when presenting the amendment proposal (transitional provisions for new series of amendments)


-           Extension to scope of ToR to C2 and C3 (GRBP-70-03)

EC explained the rationale of the request to extend the scope to C2 and C3, that is linked to the EU new General Safety Regulation (currently under co-decision procedure) requesting requirements for Wet Grip on Worn tyres for C1, C2 and C3 in UN Regulation No 117.

IWG was of the opinion that this should not be discussed in the IWG WGWT, but in GRBP.




Next meeting(s)


  •   Official sessions of IWG WGWT:

         4. Meeting: Physical (ETRTO office) + Web conference: October 18 th (10:30- 17:30):

workplan validation and implementation

         5 th Meeting: 27 (pm) - 28 (am) January GRBP – Geneva

         6 th Meeting: March 2020 – TBD

         7 th Meeting: May 2020 – TBD



The meeting was completed by drafting the presentation of the status report to the 70 th GRBP.

Chair concluded the meeting by thanking the participants for their work performed up to now, their contributions to this meeting and their availability to participate in the next meeting on 18 October.




All documents of this IWG WT are/will be available via the UNECE website: