GERMAN/ISO PROPOSAL

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Informal document No. GRRF-56-28 (56th GRRF,
20-22 September 2004, agenda item 6.2.)
Wet Grip Regulation Ad hoc GRRF conclusions
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TEST METHODS

• TWO APPROVED METHODS FOR WET GRIP EVALUATION
• Using a standard passenger car

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B. Using a Traction Trailer Tow Vehicle
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TEST METHODS

• 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).

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TESTING PARAMETERS

• 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

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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.

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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
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WET GRIP THRESHOLDS

• Ad hoc WG-GRRF proposal
•  Summer Tyres   110
•  MS  Tyres  depending on the speed
  index
• Speed Index gt Q ? threshold 100
• Speed Index lt Q ? threshold 90
• (10 better than SRTT wet grip performance)
• (equivalent to the SRTT wet grip performance)

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OF TYRES NOT MEETING THE LIMITS
Wet grip index cumulative distribution curve for
the European tyre market .
Representing more than 270 Million tyres produced
per year
cumulative
100
90
80
70
All tyres
110 Normal use
Av. w/o MS
60
highway tyres
50
100 Threshold for
40
MS gt 160 km/h
30
MS lt 160 km/h
20
10
wet grip
index
0
80
90
100
110
120
130
140
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THANK YOU FOR YOUR ATTENDANCE