Informal document No. GRRF-71-10
(71st GRRF, 13-15 September 2011
agenda item 6(d))
UNECE Regulation No 117
Testing method for measuring the wet grip index of C1 tyres
Proposed amendments
Ref ECE/TRANS/WP29GRRF/2011/12
Informal document GRRF-69-23
GRRF 71st session
Sep.13-15, 2011
The European Tyre and Rim Technical Organisation
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Tyre Industry requests to amend R.117.02 by adopting the same test method for wet grip (C1
tyre category) as the one used for labeling purpose.
Background
When EC decided to introduce an EU regulation for tyre wet grip labelling, the tyre industry checked if the
existing test method designed for Type Approval was suitable for that purpose.
The assessment made by tyre industry highlighted a too wide dispersion of the test results to comply with the
requirements of labeling scheme (bandwidth of 15%).
Design of Experiment
• One Round Robin Test performed in three sessions at different temperature to cover the full range.
• Participation: 8 companies.
• Testing surfaces: 9
• Tyre sizes: 9 (5 Normal and 4 Snow tyres)
• Test method: vehicle and trailer.
More than 300 tests over more than 10 testing surfaces have been performed by the industry to verify the new testing conditions
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UNECE R117 vs. R1222/2009 GRADING - WET GRIP TEST PROCEDURES
ROUND ROBIN TESTS - NORMAL TYRES (YEAR 2008)
TYRE SIZE
BRAND NAME
205/55 R 16
225/45 R 17
205/55 R 16
195/65 R 15
225/45 R17
BRIDGESTONE
CONTINENTAL
MICHELIN
VREDESTEIN
COOPER
SRTT TYRE SIZE
ASTM
P195/75 R 14
P225/60 R16
E 1136
F 2493 – 08
ROUND ROBIN TESTS - SNOW TYRES (YEAR 2008)
TYRE SIZE
BRAND NAME
205/55 R 16
205/55 R 16
205/55 R 16
205/55 R 16
CONTINENTAL
MICHELIN
GOODYEAR
BRIDGESTONE
The selection of the test tyres sizes was according to the most representative tyres in their
respective product segments.
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Testing Tracks Location
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Concept of the new test method
1. Use SRTT16 (Index of SRTT16 = 125)
2. Temperature adjustment and Surface Friction adjustment
3. Reference test conditions.
Wet grip index before adjustment
Temp adjustment
Test tyre
Test tyre
Adjusted index
SRTT16
Surface friction adjustment
SRTT16
SRTT16 at reference condition
(average condition)
Reference temp
Temperature during the test
Temp adjustment factor
Surface friction adjustment factor
Explanations of the above three points are given in the following slides.
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1. Use SRTT16 (Index of SRTT16 = 125)
• 2008 ETRTO Round Robin Test
ASTM 16" related to SRTT 14"
WGI (Ref : SRTT 14")
135
130
125
Avg = 125
120
115
110
105
100
18 Test conditions (7 sites, Temperature from 5 to 32 °C, Vehicle & Trailer)
Test tyre
Wet grip index before adjustment
Test tyre
Adjusted index
SRTT16
Temp adjustment
Surface friction adjustment
SRTT16
Reference temp
Temperature during the test
SRTT16 at reference
condition
(average condition)
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1. Use SRTT16 (Index of SRTT16 = 125)
Uniroyal Tiger Paw
195/75 R 14
SRRT E1136
Uniroyal Tiger Paw
225/60 R 16
ASTM F2493’08
7
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2. Temperature adjustment and Surface friction adjustment
• The test results variability of current wet grip test method in R117.02 is
mainly due to the high diversity of the sensitivity behavior of the tyres to
Track grip and Temperature parameters.
• These different sensitivities can be explained by the choice of proper
tyre design criteria addressed to different conditions of use. That is the
reason why, different treatments for snow and normal tyres are applied.
• For both normal and snow tyre the concept of temperature and friction
ADJUSTMENT is introduced, (a and b coefficient) being representative
of average variation of snow and summer categories.
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Performance vs. ASTM [%]
2 a. Temperature adjustment and Surface friction adjustment
norma
l ty
res
Performance vs. ASTM [%]
Temperature
[°C]
Temperature behavior of normal
and snow tyres are different.
Average slope of round robin tyres
for both groups leading to
adjustment factors a (see chart 6):
-0,4232 (normal) and 0,7721 (snow)
For this reason the “a” factor is
different for Normal and Snow tyres
snow t
yres
Temperature
[°C]
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Performance vs. ASTM [%]
2 b. Temperature adjustment and Surface friction adjustment
norma
l ty
res
Performance vs. ASTM [%]
µ ASTM / 0,68 [ ]
Surface friction behavior of normal
and snow tyres are different.
Average slope of round robin tyres
for both groups leading to
adjustment factors b (see chart 6):
-8,297 (normal) and +31,18 (snow)
For this reason the “b” factor is
different for Normal and Snow tyres
snow t
yres
µ ASTM / 0,68 [ ]
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3. Reference test conditions
•Temperature normalization
20 ºC for Normal tyres as middle of the range 5- 35 ºC.
10 ºC for Snow tyres as middle of the range 2-20 ºC
Note: reference temperature of 20 ºC for snow tyre is not appropriate for service
conditions and therefore the test temperature range had to be changed from 5- 35
ºC to 2-20 ºC.
• Surface normalization
0.70 which is the middle of the μ range 0.60- 0.80 (SRTT 14 μ) corresponding to
BPN=51 which is the middle of the BPN range 42-60
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Test Results from the Round Robin Test 2008-2009
Normal tyre 3
Normal tyre 2
Normal tyre 1
R117 test method application
Track 9 - Cold
Track 1 - Cold
Track 7 - Cold
Track 3 - Cold
Track 9 - Hot
Track 8 - Hot
Track 7 - Hot
Track 6 - Hot
Track 5 - Mid
Track 4 - Hot
Track 3 - Hot
Track 2 - Mid
Track 1 - Hot
New test method application
142
130
139
134
140
146
152
151
146
154
142
139
143
80
100
Track 9 - Cold
Track 1 - Cold
Track 7 - Cold
Track 3 - Cold
Track 9 - Hot
Track 8 - Hot
Track 7 - Hot
Track 6 - Hot
Track 5 - Mid
Track 4 - Hot
Track 3 - Hot
Track 2 - Mid
Track 1 - Hot
120
140
Avg / Std
143 / 7.1%
141
141
145
147
142
150
144
131
80
100
Track 9 - Cold
Track 1 - Cold
Track 7 - Cold
Track 3 - Cold
Track 9 - Hot
Track 8 - Hot
Track 7 - Hot
Track 6 - Hot
Track 5 - Mid
Track 4 - Hot
Track 3 - Hot
Track 2 - Mid
Track 1 - Hot
120
Avg / Std
138 / 8.6%
138
140
120
122
124
122
80
100
120
129
130
131
Avg / Std
124 / 5.5%
134
140
160
100
120
Avg / Std
152
147
140
142 / 4.3%
-2.8%
40%
160
132
127
139
128
144
131
139
137
143
142
Avg / Std
149
137 / 6.7%
134
135
80
126
118
119
140
141
139
Track 9 - Cold
Track 1 - Cold
Track 7 - Cold
Track 3 - Cold
Track 9 - Hot
Track 8 - Hot
Track 7 - Hot
Track 6 - Hot
Track 5 - Mid
Track 4 - Hot
Track 3 - Hot
Track 2 - Mid
Track 1 - Hot
160
126
116
138
138
141
140
145
136
146
141
80
138
124
Track 9 - Cold
Track 1 - Cold
Track 7 - Cold
Track 3 - Cold
Track 9 - Hot
Track 8 - Hot
Track 7 - Hot
Track 6 - Hot
Track 5 - Mid
Track 4 - Hot
Track 3 - Hot
Track 2 - Mid
Track 1 - Hot
160
135
121
New test method allows
to reduce significantly
Standard Deviation
100
Track 9 - Cold
Track 1 - Cold
Track 7 - Cold
Track 3 - Cold
Track 9 - Hot
Track 8 - Hot
Track 7 - Hot
Track 6 - Hot
Track 5 - Mid
Track 4 - Hot
Track 3 - Hot
Track 2 - Mid
Track 1 - Hot
120
140
-1.9%
22%
160
122
122
12
127
122
122
120
125
122
126
128
120
126
120
80
100
120
Avg / Std
123 / 2.8%
140
-2.7%
50%
160
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Test Results from the Round Robin Test 2008-2009
Normal tyre3
Normal tyre2 Normal tyre1
R117 test method application
New test method application
Test method
for Wet grip grading
Std
7.1%
Std
5.5%
4.3%
Current R117
Std
8.6%
Std
Std
6.7%
Tested on 9 different tracks
Temperature range from cold to hot
Std
2.8%
-2.8%
40%
-1.9%
22%
-2.7%
50%
New test method allows to reduce significantly Standard Deviation
The European Tyre and Rim Technical Organisation
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Test Results from the Round Robin Test 2008-2009
Snow tyre 3
Snow tyre 2
Snow tyre 1
R117 test method application
Track 7
New test method application
135
121
Track 5
137
Track 4
Avg / Std
134
Track 3
121
Track 2
132 / 11.9%
133
Track 1
80
100
120
123
Track 5
124
Avg / Std
122
135 / 13.1%
137
120
140
Track 3
121
Track 2
118
Avg / Std
124 / 7.3%
130
100
110
110
120
120
130
130
150
160
43%
140
150
160
130
128
138
Track 4
Avg / Std
136
Track 3
Track 2
137 / 8.6%
134
138
90
100
110
120
130
120
140
-4.5%
34%
150
160
14
122
124
Track 4
Avg / Std
134
127 / 4.9%
123
Track 3
129
Track 2
80
90
100
110
120
130
-2.4%
33%
131
Track 1
140
-5.1%
133
Track 5
Track 1
90
100
Track 6
134
80
90
Track 7
Track 4
134 / 6.8%
133
80
120
Track 5
132
160
115
Track 6
Track 2
Avg / Std
Track 1
123
Track 7
132
Track 5
Track 1
100
Track 3
Track 7
136
80
136
Track 4
80
139
Track 2
126
Track 6
Track 4
Track 3
Track 5
160
137
Track 6
Track 6
127
Track 1
140
Track 7
136
Track 7
119
Track 6
New test method allows
to reduce significantly
Standard Deviation
140
150
160
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Test Results from the Round Robin Test 2008-2009
Snow tyre 3
Snow tyre 2
Snow tyre 1
R117 test method application
Test method
for Wet grip grading
Std
11.9%
Std
New test method application
Current R117
13.1%
Std
7.3%
Std
6.8%
Std
8.6%
Tested on 9 different tracks
Temperature range from cold to hot
Std
4.9%
-5.1%
43%
-4.5%
34%
-2.4%
33%
New test method allows to reduce significantly Standard Deviation
The European Tyre and Rim Technical Organisation
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Summary
Normal tyres
Snow tyres
Improvement Action
Current Reg117
Test Method for WetGrip Grading
Test Method for WetGrip Grading
Quality Target
Item not covered
Weighted standard deviation<=5%
Weighted standard deviation<=5%
Reference Tire
SRTT14
ASTM 16=125%
ASTM 16=125%
Differentiate Normal/Snow
grading scheme
not mentioned
No
No
Differentiate Normal/Snow
testing conditions
not mentioned
Yes
Yes
Wet surface
Temperature Range
5-35 °C
5-35 °C
2-20 °C
Ambient
Temperature Range
not mentioned
5-35 °C close to water temp
(10°C max. difference)
2-20°C close to water temp
(10°C max. difference)
BPN Range
40-60
as Reg117 for skid trailer mu (0.6-0.8)
corresponding BPN range 42-60
as Reg117 for skid trailer mu (0.6-0.8)
BPN range 42-60
Correction Factor introduction for
Wet Grip Index
(Friction and Temperature)
not mentioned
Yes Both different between
normal & snow tyres
Yes Both different between
normal & snow tyres
Reference conditions
not mentioned
for vehicle (20°C, 0.68 mfdd)
for trailer (20°C, 0.85 pbfc)
for vehicle (10°C, 0.68 mfdd)
for trailer (10°C, 0.85 pbfc)
Pros
(by column)
reliable for
homologation
the method is valid for both
normal & snow tyres
the method is valid for both
normal & snow tyres
BPN= British pendulum Number mfdd= mean fully developed deceleration
pbfc= peack braking force coefficient
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Conclusion
Advantages of a single wet grip test method (C1 tyre category):
•
Reduces the test results dispersion.
New Test method
Current R117
•
•
•
Introduces an SRTT Rim code 16 that fits better on the current vehicle mountings (size
much closer to current tyre sizes). This reduces the need to use an intermediate control
tyre.
1/17
Cost saving: CoP test results can be used for market surveillance in the frame of tyre
labelling.
Cost reduction for Tyre Industry due to adoption of a single test method.
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Annex
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Basic concept of R117 and new Test method
80km/h 20km/h Deceleration G
Water film 0.5-1.5mm
19
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Modified truck (on the center of floor, we can add additional tyre axle which the
test tyre will be attached.)
tyre test vehicle
Test position
20
65 km/h Peak Braking Force Coefficient
Water film 0.5-1.5mm
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Tow vehicle and trailer
Test tyre
Tow vehicle
Test position
Only this tyre is under brake
trailer
Test position
65 km/h Peak Braking Force Coefficient
Water film 0.5-1.5mm
Provided by Continental
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BPN measurement
22
Rubber piece
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End
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