wet grip regulation ad hoc grrf conclusions

GRRF 56 September 2004 11

Wet Grip Regulation

Ad hoc GRRF conclusions

Informal document No. GRRF-56-28

(56th GRRF, 20-22 September 2004,

agenda item 6.2.)


1) TWO APPROVED METHODS FOR WET GRIP EVALUATION

A. Using a standard passenger car

TEST METHODSTEST METHODS


B. Using a Traction Trailer & Tow Vehicle


1) 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 1136 - 195/75 R 14).

TEST METHODSTEST METHODS


3) 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 : 0.7 + 0.3 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 PARAMETERSTESTING PARAMETERS


Evaluation of the Method

• The Round-Robin tests of TÜV automotive and the tyre industry produced good repeatable results.

• ConclusionsThe SRTT performance seems to be The SRTT performance seems to be

constant on the same test track constant on the same test track without being influenced remarkably without being influenced remarkably by further test conditionsby further test conditions

The evaluation of the wet grip will be The evaluation of the wet grip will be performed on a relative performed on a relative performance.performance.

The percentage relation between test The percentage relation between test tyres and SRTT (Index (R(T)) tyres and SRTT (Index (R(T)) remains very constant on the same remains very constant on the same track even under different track even under different temperatures.temperatures.

60

80

100

120

140

160

180

200

SRTT T1 T2 SRTT T3 T4 SRTT

Wet

gri

p in

dex

March 2001 Temperature : 15-24°C

June 2001 Temperature : 24-37°C

March 2001 Temperature : 15-24°CJune 2001 Temperature : 24-37°CDistance (m) Index (%) Distance (m) Index (%)

SRTT 49,2 100 60,1 100T1 33,6 147 40,9 148T2 34 146 42,4 143

SRTT 49,9 100 61,2 100T3 32,3 154 39,8 154T4 38,6 128 46,1 133

SRTT 49 100 61,3 100

Big effect on absolute values, but really small effect on index value only using a SRTT as reference tyre.


Tyre Industry Round Robin Tests

E T R T O F irst G ro upP i - B /F

V eh icle M eth o d

E T R T O S eco n d G ro upG Y -D u n lo p -C O N T I-M i

V eh icle m eth o d

J A T M A T h ird G ro up6 T y re M a n u fa ctu rer s

V eh icle M eth o dT ra iler m eth o d

3 G R O U P SE T R T O = >2J A T M A = > 1

CONCLUSIONSBased on the round-robin test data, the difference between the best and worst wet Based on the round-robin test data, the difference between the best and worst wet

grip performance tyres can be easily indentifiedgrip performance tyres can be easily indentified


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)


% OF TYRES NOT MEETING THE LIMITS

0

10

20

30

40

50

60

70

80

90

100

80 90 100 110 120 130 140

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


THANK YOU

FOR YOUR ATTENDANCE

wet grip regulation ad hoc grrf conclusions

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