1. Tyre Industry workplan proposal to IWG Worn tyres
Document WT-01-03
Agenda items: 5, 6 and 7
Tyre Industry workplan proposal to IWG Worn tyres
European Tyre and Rim Technical Organisation

2. Definition of worn tyre Preparation of a worn tyre
SUMMARY
Introduction
Definition of worn tyre
Preparation of a worn tyre
Test procedure for the evaluation of wet grip performance of a worn tyre
Moving forward – IWG agreement and assessment
European Tyre and Rim Technical Organisation

3. European Tyre and Rim Technical Organization
1. Introduction
This tyre industry position has been built by an ETRMA/ETRTO joint Task Force.
A first proposal of the group consists in prioritizing the scope of France’s proposal because of the tight timing of the IWG:
Our proposal is to built this regulation for all C1 tyres, but assess if snow tyres require a different procedure and maybe should be defined in a second step.
A certain number of test parameters have to be assessed by the IWG (see next slides).
European Tyre and Rim Technical Organization

4. European Tyre and Rim Technical Organisation
2. Definition of worn tyre
The starting point is the definition of the worn tyre.
Our Task force considers the following parameters should be assessed for a tyre in the worn state:
Tread depth
The definition of tread depth shall be assessed in respect to
the current regulatory requirements for minimum tread depth (both homologation and national prescriptions of usage) and
to the buffing tolerance of the existing machines.
Hence, the proposal is to consider, for the central part of the tread (75% of the tread width) , a tread depth of (1.6 + α) mm, being α the buffing tolerance (see worn tyre preparation part 3).
Wear profile (flat, shoulder or centreline wear)
Assessment of the influence of the wear profile on the performance at same-volume void ratio in the worn state, in particular the shoulder wear profile curvature
c. Ageing
Assessment of ageing on the worn tyre wet grip performance, and a decision or not to integrate the ageing in the preparation method
European Tyre and Rim Technical Organisation

5. 3. Preparation of a worn tyre
The use of the standard guide ASTM F (2015) raises some issues to be solved
Shall the definition of the worn tyre (see content in part 2) be integrated in the regulation text or in the tyre preparation standard ?
The final surface condition has to be representative, (wet-grip performance comparison with natural worn tyres) and in this respect has to be defined more precisely : criteria for reception and tolerance.
To define the necessary tyre buffing tolerance that is achievable, and reproducible, and repeatable.
IWG has to check the industrial feasibility and affordability of the tyre buffing (including tolerance) taken into account all these parameters of definition of the worn tyre state (see part 2) and final surface condition as defined above.
The preferred approach of EU Tyre Industry would be, when a solid and viable test procedure is created, to implement it in the UN R117 regulation while, in parallel, work at ISO level in order to grant a global robust and harmonized technical basis.
European Tyre and Rim Technical Organisation

6. European Tyre and Rim Technical Organisation
4. Test procedure for evaluating WET grip performance of a Worn tyre
Tyre Industry suggest to consider as starting point the proposed revision of the Wet Grip test method for C1 (see informal document GRB and ISO CD 23671)
An assessment is needed on certain specific parameters to confirm whether the methodologies for the evaluation of Wet grip index performance of NEW tyres can be used (dispersion, feasibility) also for WORN tyres or if a revision of these methodologies is needed.
In this respect, tyre industry proposes to investigate the impact of the following parameters on the test.
Reference tyre(s) – New state or worn state ?
Validity of the correction formulas (track friction, temperature )
Water depth window
vehicle and trailer test
Speed of test
Tyre size effect
Clusters to be considered ?
European Tyre and Rim Technical Organisation

7. 5. Moving forward – IWG agreement and assessment
Agreement on the proposed plan
Agreement on the three parameters for the definition of a worn tyre (part 2)
Assessment of the influence of the shoulder wear profile on Worn Tyre wet grip
Assessment of tread depth
Assessment on Ageing effect
Worn tyre preparation
Assessment on buffing tolerance (linked to the end of life tread depth)
Assessment of the surface roughness
Wet grip test method for evaluating worn tyre
Agreement in referring to the proposed revision of the C1 Wet Grip test method as starting point
Agreement in investigating the parameters listed in part 4
Agreement for a round robin evaluation
Next step to be considered after the test method has been defined, the IWG to launch an estimation of the current market situation on worn wet grip, in order to prepare future discussion on the threshold definition
European Tyre and Rim Technical Organisation

8. Thank you
European Tyre and Rim Technical Organisation