GRRF 56 September Wet Grip Regulation Ad hoc GRRF conclusions Informal document No. GRRF (56th GRRF, September 2004, agenda item 6.2.)

GRRF 56 September )TWO APPROVED METHODS FOR WET GRIP EVALUATION A.Using a standard passenger car TEST METHODS

GRRF 56 September B. Using a Traction Trailer & Tow Vehicle

GRRF 56 September ) TWO RECOGNISED METHODS FOR WET GRIP EVALUATION Method using a standard passenger car Trailer Method 2) BOTH METHODS EVALUATE TYRE WET GRIP The evaluation of the wet grip will be performed on a relative performance basis compared to the SRTT Tyre (ASTM E /75 R 14). TEST METHODS

GRRF 56 September ) TRACK GENERAL SPECIFICATION Two methods for measuring wetted friction surface: BPN or SRTT ‾BPN method is a dynamic pendulum impact tester used to measure the frictional properties of a surf ‾The SRTT method measures the peak braking coefficient and is averaged over six test runs. Maximum chipping size from 8 to 13 mm Sand depth : mm 4) WATER DEPTH Flooded : between 0.5 and 1.5 mm using either track-side or vehicle/trailer mounted wetting apparatus 5) CONTROL TYRE : For the vehicle method, possible use of a control tyre in conjunction with the reference tyre TESTING PARAMETERS

GRRF 56 September Evaluation of the Method The Round-Robin tests of TÜV automotive and the tyre industry produced good repeatable results. Conclusions The SRTT performance seems to be constant on the same test track without being influenced remarkably by further test conditions The evaluation of the wet grip will be performed on a relative performance. The percentage relation between test tyres and SRTT (Index (R(T)) remains very constant on the same track even under different temperatures. Big effect on absolute values, but really small effect on index value only using a SRTT as reference tyre.

GRRF 56 September Tyre Industry Round Robin Tests CONCLUSIONS Based on the round-robin test data, the difference between the best and worst wet grip performance tyres can be easily indentified

GRRF 56 September 20048

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10 WET GRIP THRESHOLDS Ad hoc WG-GRRF proposal: “ Summer Tyres ” : 110 * “ M+S Tyres” : depending on the speed index Speed Index > Q  threshold = 100 ** Speed Index < Q  threshold = 90 * (10% better than SRTT wet grip performance) ** (equivalent to the SRTT wet grip performance)

GRRF 56 September % OF TYRES NOT MEETING THE LIMITS All tyres Av. w/o M+S Wet grip index cumulative distribution curve for the European tyre market. Representing more than 270 Million tyres produced per year wet grip index cumulative % 100 = Threshold for M+S > 160 km/h M+S < 160 km/h 110 = Normal use highway tyres

GRRF 56 September THANK YOU FOR YOUR ATTENDANCE