T h e E u r o p e a n T y r e a n d R i m T e c h n i c a l O r g a n i s a t i o n UNECE Regulation No 117 Testing method for measuring the wet grip index.

T h e E u r o p e a n T y r e a n d R i m T e c h n i c a l O r g a n i s a t i o n

UNECE Regulation No 117

Testing method for measuring the wet grip index of C1 tyresProposed amendments

Ref ECE/TRANS/WP29GRRF/2011/12Informal document GRRF-69-23

GRRF 71st session Sep.13-15, 2011

1

Informal document No. GRRF-71-10(71st GRRF, 13-15 September 2011agenda item 6(d))


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.

BackgroundWhen 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%).

2

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.

More than 300 tests over more than 10 testing surfaces have been performed by the industry to verify the new testing conditions


ROUND ROBIN TESTS - NORMAL TYRES (YEAR 2008)

TYRE SIZE 205/55 R 16 225/45 R 17 205/55 R 16 195/65 R 15 225/45 R17

BRAND NAME BRIDGESTONE CONTINENTAL MICHELIN VREDESTEIN COOPER

ROUND ROBIN TESTS - SNOW TYRES (YEAR 2008)

TYRE SIZE 205/55 R 16 205/55 R 16 205/55 R 16 205/55 R 16

BRAND NAME CONTINENTAL MICHELIN GOODYEAR BRIDGESTONE

SRTT TYRE SIZE P195/75 R 14 P225/60 R16

ASTM E 1136 F 2493 – 08

UNECE R117 vs. R1222/2009 GRADING - WET GRIP TEST PROCEDURES

The selection of the test tyres sizes was according to the most representative tyres in their respective product segments.

3


4

Testing Tracks Location


Wet grip index before adjustment Temp adjustment Surface friction adjustment

SRTT16

Test tyreTest tyre

Adjusted index

Temperature during the testReference temp

SRTT16

SRTT16 at reference condition(average condition)

Concept of the new test method

1. Use SRTT16 (Index of SRTT16 = 125)2. Temperature adjustment and Surface Friction adjustment 3. Reference test conditions.

Explanations of the above three points are given in the following slides.

Temp adjustment factorSurface friction adjustment factor

5


6

• 2008 ETRTO Round Robin Test

ASTM 16" related to SRTT 14"

100

105

110

115

120

125

130

135

18 Test conditions (7 sites, Temperature from 5 to 32 °C, Vehicle & Trailer)

WG

I (R

ef

: S

RT

T 1

4")

Avg = 125

Wet grip index before adjustment Temp adjustment Surface friction adjustment

SRTT16

Test tyreTest tyre

Adjusted index

Temperature during the testReference temp

SRTT16

SRTT16 at reference condition(average condition)

1. Use SRTT16 (Index of SRTT16 = 125)


7

Uniroyal Tiger Paw195/75 R 14SRRT E1136

Uniroyal Tiger Paw225/60 R 16ASTM F2493’08

1. Use SRTT16 (Index of SRTT16 = 125)

7


• 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.

2. Temperature adjustment and Surface friction adjustment

8


9

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

normal tyres

snow tyres

Temperature [°C]

Temperature [°C]

Per

form

an

ce v

s. A

ST

M [%

]P

erfo

rma

nce

vs.

AS

TM

[%]

2 a. Temperature adjustment and Surface friction adjustment


10

normal tyres

snow tyres

Per

form

an

ce v

s. A

ST

M [%

]P

erfo

rma

nce

vs.

AS

TM

[%]

µ ASTM / 0,68 [ ]

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

2 b. Temperature adjustment and Surface friction adjustment


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

11


Test Results from the Round Robin Test 2008-2009

12

142130

139134

140146

152151

146154

142139

143

80 100 120 140 160

Track 1 - HotTrack 2 - MidTrack 3 - HotTrack 4 - HotTrack 5 - MidTrack 6 - HotTrack 7 - HotTrack 8 - HotTrack 9 - HotTrack 3 - ColdTrack 7 - ColdTrack 1 - ColdTrack 9 - Cold

135121

138124

141141

145147

142150

144131

138

80 100 120 140 160


126116

126118119

129130131

120134

122124

122

80 100 120 140 160


138138

141140

145136

146141

152147

140141139

80 100 120 140 160


135134

142143

149137

139131

144128

139127

132

80 100 120 140 160


120126

120128126

122125

120122122

127122122

80 100 120 140 160


Avg / Std

143 / 7.1%

Avg / Std

138 / 8.6%

Avg / Std

124 / 5.5%

Avg / Std

123 / 2.8%

Avg / Std

142 / 4.3%

Avg / Std

137 / 6.7%

New test method allows to reduce

significantly Standard Deviation



-2.8%

40%

-1.9%

22%

-2.7%

50%

Norm

al ty

re

1N

orm

al ty

re

2N

orm

al ty

re

3

New test method applicationR117 test method application

12


13

Std

7.1%

Std

8.6%

Std

5.5%Std

2.8%

Std

4.3%

Std

6.7%

New test method allows to reduce significantly Standard Deviation


-2.8%

40%

-1.9%

22%

-2.7%

50%

Norm

al

tyre

1N

orm

al

tyre

2N

orm

al

tyre

3New test method applicationR117 test method application

Tested on 9 different tracksTemperature range from cold to hot

Current R117

Test method for Wet grip grading



14

133

121

134

137

121

119

135

80 100 120 140 160

Track 1

Track 2

Track 3

Track 4

Track 5

Track 6

Track 7

137

122

136

139

124

123

137

80 100 120 140 160

Track 1

Track 2

Track 3

Track 4

Track 5

Track 6

Track 7

123

115

120

134

121

118

130

80 90 100 110 120 130 140 150 160

Track 1

Track 2

Track 3

Track 4

Track 5

Track 6

Track 7

Avg / Std

132 / 11.9%

Avg / Std

135 / 13.1%

Avg / Std

124 / 7.3%

Avg / Std

127 / 4.9%

Avg / Std

134 / 6.8%

Avg / Std

137 / 8.6%

-5.1%

43%

-4.5%

34%

-2.4%

33%

Sn

ow

tyre

1S

now

tyre

2S

now

tyre

3


136

127

126

136

132

132

133

80 90 100 110 120 130 140 150 160

Track 1

Track 2

Track 3

Track 4

Track 5

Track 6

Track 7

133

130

128

138

136

134

138

80 90 100 110 120 130 140 150 160

Track 1

Track 2

Track 3

Track 4

Track 5

Track 6

Track 7

131

129

123

134

124

122

120

80 90 100 110 120 130 140 150 160

Track 1

Track 2

Track 3

Track 4

Track 5

Track 6

Track 7

Test Results from the Round Robin Test 2008-2009New test method allows to reduce




14


15

Std

11.9%

Std

13.1%

Std

7.3%Std

4.9%

Std

6.8%

Std

8.6%

-5.1%

43%

-4.5%

34%

-2.4%

33%

Sn

ow

tyre

1S

now

tyre

2S

now

tyre

3


Tested on 9 different tracksTemperature range from cold to hot



Current R117

Test method for Wet grip grading



Summary

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/Snowgrading scheme

not mentioned No No

Differentiate Normal/Snowtesting conditions

not mentioned Yes Yes

Wet surfaceTemperature Range

5-35 °C 5-35 °C 2-20 °C

AmbientTemperature Range

not mentioned5-35 °C close to water temp

(10°C max. difference)2-20°C close to water temp

(10°C max. difference)

BPN Range 40-60as Reg117 for skid trailer mu (0.6-0.8)

corresponding BPN range 42-60as 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 betweennormal & snow tyres

Yes Both different betweennormal & snow tyres

Reference conditions not mentionedfor 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 forhomologation

the method is valid for bothnormal & snow tyres

the method is valid for bothnormal & snow tyres

Normal tyres Snow tyres

BPN= British pendulum Number mfdd= mean fully developed deceleration pbfc= peack braking force coefficient

16


• Reduces the test results dispersion.

• 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.

• 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.

Current R117

New Test method

Conclusion

Advantages of a single wet grip test method (C1 tyre category):

17

1/17


18

Annex


19

80km/h 20km/h Deceleration GWater film 0.5-1.5mm

Basic concept of R117 and new Test method

19


20

Test position

Modified truck (on the center of floor, we can add additional tyre axle which the test tyre will be attached.)

tyre test vehicle

65 km/h Peak Braking Force CoefficientWater film 0.5-1.5mm

20


21

Test position

Test positionOnly this tyre is under brake

Tow vehicle and trailer

Tow vehicle

trailer

Test tyre

Provided by Continental

65 km/h Peak Braking Force CoefficientWater film 0.5-1.5mm


22

BPN measurement

Rubber piece

22


23

End

T h e E u r o p e a n T y r e a n d R i m T e c h n i c a l O r g a n i s a t i o n UNECE Regulation No 117 Testing method for measuring the wet grip index.

Documents

n t y r e

n d r i

t h e e u r o p e

t e c h n i c

t i o n unece regulation

t i o n design of experiment

t i o n wet grip index

tyre size20555 r