Use of the ASTM SRTT for Standardized OBSI Measurement

Paul R. DonavanIllingworth & Rodkin, Inc..

OBSI WorkshopTRB 89th Annual Meeting

US Standard Test Tire MigrationGoodyear Aquatred 3

P205/70R15UniRoyal SRTT

P225/60R16

Issues for a Benchmark Tire

n Long term & international availability

n Variation between “identical” tires

n Change in noise generation over time

n Break-in & warm-up period

n Relationship to other, in-service tires

ATSM Standard Reference Test

Tire (SRTT)

n SRTT To be constructed for 10 years

n UniRoyal Tiger Paw brand, supplier is Michelin

n Use in the US & Europen Can be ordered

internationally n Relatively high cost tire

SRTT Specification

n Durometer hardness Type A – 64 ± 2Equilibrium temperature – 73.4ºF ± 3.6ºAverage of 4 ribs – center rib excluded

n Storage Not to exceed 70ºFLimit ozone exposure

n Wheel rim width – 6.5” ± 0.5”n Current cost ~ $400

Tire-to-Tire Variation

nSix tires of different age/mileage Two used in testing previously (~700 & 125 mi)Four new to be used for passby testing

nPavements (7 total)DGAC – one typical (two directions), one courseOGAC – two directions of travelPCC – one longitudinally tined, one ground

nAverage of three runs

SRTT Test Tires (2007)

Designation Manufacturer Date

Purchase Date Application Km at

StartAverage

Hardness

SRTT #1 Oct-05 Mar-06 Secondary OBSI ~ 1000 63

SRTT #2 Oct-05 Mar-06 Primary OBSI ~ 200 64

LF Passby Jul-06 Oct-06 Passby tire 0 64

LR Passby Jul-06 Oct-06 Passby tire 0 65

RF Passby Jul-06 Oct-06 Passby tire 0 64

RR Passby Jul-06 Oct-06 Passby tire 0 64

Date of Testing = May 2007

SRTT Tire-to-Tire Variation (2007)

96

97

98

99

100

101

102

103

104

105

DGACEB

OGACEB

OGACWB

DGACWB

Long.TinedPCC

GroundPCC

AC

Soun

d In

tens

ity L

evel

, dB

A

SRTT #1SRTT #2LF Passby TireLR Passby TireRF Passby TireRR Passby Tire

Ranges – 0.5 to 1.1 dBAverage Range – 0.8 dBAverage Standard Deviation – 0.3 dB

SRTT Test Tires – 2007 & 2008

Designation Manufacturer Date

Purchase Date Application Km at

StartAverage

Durometer

SRTT #1 Oct-05 Mar-06 Primary OBSI ~ 1000 63

SRTT #2 Oct-05 Mar-06 Secondary OBSI ~ 200 64

LF Passby Jul-06 Oct-06 Passby tire 0 64LR Passby Jul-06 Oct-06 Passby tire 0 65

RF Passby Jul-06 Oct-06 Passby tire 0 64

RR Passby Jul-06 Oct-06 Passby tire 0 64SRTT #1 Oct-05 Mar-06 Secondary OBSI ~ 2000 66

RR Passby Jul-06 Oct-06 Passby tire ~ 300 63

SRTT #3 Oct-07 Oct-08 New Backup 0 62

SRTT Tire-to-Tire Variation (2008)

97

98

99

100

101

102

103

104

97 98 99 100 101 102 103 104

Sound Intensity Level, dBA - SRTT #1

Soun

d In

tens

ity L

evel

, dB

A

RR Passby Tire (std dev = 0.2 dB)

SRTT #3 (std dev = 0.3 dB)

1 to 1 Line

Change in Noise over Time

nTire durometer hardness (tire aging)Noise increases with hardnessHardness increases with agingReported effect ~ 2 dB per 10 durometer numbersHardness increases at higher rate with exposure to higher temperature and ozone amounts

nTread depth (tire wear)Inconsistent trendsResults varying with test surface

nVery limited data specific to the SRTT

92

94

96

98

100

102

104

106

DGAC EB OGAC EB OGAC WB DGAC WB Long. TinedPCC

Ground PCC

Soun

d In

tens

ity L

evel

, dB

A

SRTT #1 2007SRTT #1 2008RR Passby Tire 2007RR Passby Tire 2008

Variation in Level 5/2007 to 10/2008

Variation by Tire & Age

97

98

99

100

101

102

103

104

105

Apr 07 Oct 07 Nov 07 Oct 08 Oct 09Date of Test

Ove

rall

OB

SI L

evel

, dB

A

SRTT 1 Passby SRTTSRTT 2 SRTT 3NCHRP SRTT

Burlap Drag PCC

Variation by Tire & Age

97

98

99

100

101

102

103

104

105

Apr 07 Oct 07 Nov 07 Oct 08 Oct 09Date of Test

Ove

rall

OB

SI L

evel

, dB

A

SRTT 1 Passby SRTT

SRTT 2 SRTT 3

NCHRP SRTT

Ground PCC

Tire ComparsionsGoodyear Aquatred 3

P205/70R15UniRoyal SRTT

P225/60R16

Dunlop SP Winter Sport 3 P225/60R16

Comparison of Tire OBSI Levels

96

97

98

99

100

101

102

103

104

105

106

107

108

109

110

95 96 97 98 99 100 101 102 103 104 105 106 107 108 109

Sound Intensity Level, dBA - SRTT

Soun

d In

tens

ity L

evel

, dB

A

Aquatred (std dev = 0.3 dB)

Dunlop M3 (std dev = 0.6 dB)

1 to 1 Line

Comparison to SPB Results

n12 sites measured nMix of AC and PCCnMeasured

Statistical passbys for light vehiclesControlled passbys for test vehicle with SRTT tires

nExamples for 7.5m microphonePCC – longitudinally tinesDGAC – 5 years oldPorous AC – 1 year old

SRTT CPB & SPB Results - DGAC

65

70

75

80

85

90

95

70 80 90 100 110 120 130

Speed, km/hr

Soun

d Pr

essu

re L

evel

, dB

A

CPB with SRTT

Light Vehicle SPB

SRTT CPB & SPB Results – Porous AC

65

70

75

80

85

90

95

70 80 90 100 110 120 130

Speed, km/hr

Soun

d Pr

essu

re L

evel

, dB

A

CPB with SRTT

Light Vehicle SPB

SRTT CPB & SPB Results – PCC

65

70

75

80

85

90

95

70 80 90 100 110 120 130

Speed, km/hr

Soun

d Pr

essu

re L

evel

, dB

A

CPB with SRTT

Light Vehicle SPB

SRTT CPB & SPB Results – 12 Sites

70

72

74

76

78

80

82

84

86

88

90

70 72 74 76 78 80 82 84 86CPB Sound Pressure Level, dBA

SPB

Sou

nd P

ress

ure

Leve

l, dB

A

Constant Offset Fit:Offset = 2.7 dB

Std Dev = 0.9 dB

y = 0.93x + 7.81R2 = 0.93

OBSI & CPB for “Hard” Sites – 25 ft

66

68

70

72

74

76

78

80

82

84

88 90 92 94 96 98 100 102 104 106 108OBSI Level, dBA

Soun

d Pr

essu

re L

evel

, dB

A

Medium Texture

Fine Texture

Transverse Texture

Constant Offset

Linear Regression

Slope = .94R2 = 0.94Offset = 23.7Std Dev = 0.9

Summary:

SRTT as a benchmark tire

nLong term availabilitynRank orders pavements similar to other tires

(lower absolute levels)nLow tire-to-tire variation

Varies with pavementAverage range of 6 tires = 0.8 dB

nPerformance maintained under moderate usage up to at least 1½ years