Assessment of the current requirements and testing procedures of UNECE Regulation 117

As part of JRC research on vehicle safety in normal conditions of use and under real driving conditions, we carried out a test campaign on three C1 tyres (i.e. tyres for passenger cars) for wet braking performance in “New” and “Worn” state, based on the wet grip test of UNECE Regulation 117. The purpose is to identify possible shortcomings and weaknesses of the current regulatory requirements and testing procedures for future possible amendments. In addition, this work also allowed to gain experience with new regulatory tests and to perform a comparative analysis between new and worn tyres with different production dates. First, for each model, we procured tyre samples with “Recent” (i.e. within 2 years from the tests) and “Aged” (4 years from the test) production dates. We tested some new tyres for wet grip according to the UNECE Regulation 117 under the market surveillance framework (Regulation (EU) 2018/858). Then we artificially wore the tyres by buffing (i.e. removing tread material with a machine as described in the Regulation 117) and performed additional wet grip tests for worn tyres based on the new amendments of UNECE Regulation 117. In both wet grip tests (i.e. new and worn tyres) we performed tests on two sets for each tyre model: “Recent” and “Aged”. We calculated the wet grip indexes of new and worn state samples and evaluated the performance drop between the two states. Finally, we assessed the capability of tyres on the market to pass the wet grip regulatory test in worn state. No tyres in new state showed any statistically significant difference between “Aged” and “Recent” samples, while in the worn state, “Recent” Tyre 1 samples braked 4.5 m longer than “Aged” ones. As tyres were considered a “black box” in this study (i.e. no information on compound and structure properties are available), it was not possible to establish the reasons of this performance change. However, this strengthens the need – in case of suspicious behaviour of a tyre tested – for increasing market surveillance tests for that tyre model during its whole life on the market, to ensure that tyres always offer a fairly constant level of safety both during the life of an individual tyre and during the commercial life of the tyre model. The average performance drop between the wet grip index in new and worn state found in our tests was 24%, sensibly lower than the one in ETRTO findings (34%). This result has to be backed by further research and larger data collection. If this result is confirmed, our market assessment estimates that ≈23454 more C1 tyre models out of the 104227 currently on the market would pass the newly introduced regulatory test, corresponding to ≈23% more tyre models on the market.