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1l TIE

DEFLECTION ON TRUCK TIRE NOISE LBJEL1

R.D. Kilmer

M.A. Cadoff

D.E. Mathews

C.O. Shoemaker, Jr.

National Bureau of Standards

Department of Commerce

Washington, D.C. 20234

^SJTS W-MO

Contract 110. 00T -AS-60031

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100

.U56

78-157C

JANUARY 1979

FINAL REPORT

Document is available to the U.S. public through

The National Technical Information Service,

Springfield, Virginia 22161

Prepared For

U.S. DEPARTMENT OF TRANSPORTATION

National Highway Traffic Safety Administration

Washington, D.C. 20590

c.2
*-

r
TECHNICAL REPORT STANDARD TITLE PAGE

1* Report No. DOT-HS-803 8742. Govcrnmtnt Accession No. 3. Recipient's Catalog No.

4. Titla and Subtitle Effects of Load, Inflation Pressure and Tire

Deflection on Truck Tire Noise Levels

5. Report Date Januarv 1979

6. Performing Organization Code

7. Author*.) R< D< Kilmer> M> A> cadoff, D. E. Mathews,

C. 0. Shoemaker, Jr.

8. Performing Organization Report No. NBSIR 78-1570

9. Performing Orgonizotion Nome and Address National Bureau of Standards

Department of Commerce

Washington, D. C. 20234

10. Work Unit No.

11. Contract or Gront No. DOT-AS-60031

13. Type of Report and Period Covered FINAL

May 1975-November 1978

12. Sponsoring Agency Nome ond Address Department of Transportation*

Office of the Secretary

Office of Noise Abatement

Washington, D. C. 20590

14. Sponsoring Agency Code

15. Supplementary Note* * Now the Office of Heavy Duty Vehicle Research of the

National Highway Traffic Safety Administration

16.

Ab.troctSAE Recommended Practice J57a — Sound Level of Highway Truck Tires -- specifies that the tests be made using tires inflated to the maximum inflation

pressure and loaded to the maximum load as specified by the Tire and Rim

Association (T&RA). However, if local load limits preclude the use of the

maximum rated load,, tests may be conducted using lower loads if the

inflation pressure ‘is adjusted either to maintain constant tire deflection or according to the T&RA load/inflation pressure tables. Whether these alternate

load/inflation pressure conditions result in similar sound levels is an important

question. This report presents acoustic data that allows evaluation of the

equivalency of these alternate conditions. In addition, laboratory data on the

relationships between load, inflation pressure, and tire deflection are presented.

On the basis of these data, for tire loads greater than 70 to 75 percent of the

maximum rated load, smaller variations of the measured sound level were observed

when constant inflation pressure was maintained than when the inflation pressure

was adjusted. This is convenient since this essentially represents the typical

in-service case where the load varies between trips but the tire inflation

pressure is maintained at a constant value.

17.

Key Words Acoustics; noise measurement; noise

(sound); tire noise; transportation

noise; truck.

18.

Distribution Stotement Document is available to the U.S. public

through the National Technical Information

Service, Springfield, Virginia 22161

19. Security Classif. (of this report) 20. Security Classif. (of this page) 21- No. of P ages 22. Price

Unclassified Unclassified 48

Form DOT F 1700.7 (8-69)

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Abstract

RAE Recommended Practice J57a — Sound Level of Highway Truck Tires —

specifies that the tests be made using tires inflated to the maximum inflation

pressure and loaded to the maximum load as specified by the Tire and Rim

Association (T&RA). However, if local load limits preclude the use of the

maximum rated load, tests may be conducted using lower loads if the

inflation pressure is adjusted either to maintain constant tire deflection

or according to the T&RA load/ inflation pressure tables. Whether these

alternate load/ inflation pressure conditions result in similar sound levels is an important question. This report presents acoustic data that allows

evaluation of the equivalency of these alternate conditions. In addition,

laboratory data on the relationships between load, inflation pressure, and

tire deflection are presented. On the basis of these data, for tire loads

greater than 70 to 75 percent of the maximum rated load, smaller variations of

the measured sound level were observed when constant inflation pressure was maintained than when the inflation pressure was adjusted. This is convenient

since this essentially represents the typical in-service case where the load

varies between trips but the tire inflation pressure is maintained at a constant value.

4

i

iii
Acknowledgements

The authors would like to recognize the contributioris made by the

following organizations which have greatly aided this program: the staff of

the U. S. Army Yuma Proving Ground especially Mr. Francis E. Northon and Mr.

Elmer Hockman; and the American Trucking Association, Inc. member fleets —

Motor Freight Express and Davidson Transfer and Storage Company — for the

loan of test tires.

The authors also express appreciation to Mr. N. Halsey for supervision of

the load/deflection tests, to Mr. R. L. Fisher for his assistance in data

reduction and analysis, to Mrs. M. J. Hildebrand, Mrs. C. J. Stull and Mrs. D.

A. Neal for typing and preparation of the manuscript, and to Mr. W. A.

Leasure, Jr. of the U. S. Department of Transportation and Dr. G. R. Thurman

for their review and comments.

iv
Table of Contents

Page

1. Introduction ................ l

2. Load/Inflation Pressure/Deflection Study .......... 4

2.1 Test Set-Up ............ ..... 4

2.2 Test Procedures/Results ..... 8 a. Varying Load and Inflation Pressure - T&RA .... 8

b. Constant Inflation 8 c. Constant Deflection ...... 8

d. Tire Footprints ............ 13

2.3 Discussion of Test Results 13

a. Varying Load and Inflation Pressure - T&RA .... 13

b. Constant Inflation 16

c. Constant Deflection 16

d. Tire Footprints 18

3. Acoustical Measurement Program 20

3.1 Acoustical Measurement Results ..... 21

3.2 Conclusions ..... 27 *

4. Appendix A. SAE Recommended Practice for Measurement of

Truck Tire Noise 28

5. Appendix B. Acoustical Measurement Test Program 30

5.1 Field Test Site 30

5.2 Test Tires 30

5.3 Test Vehicle 35

5.4 Test Procedure 35

6. References 41

v

1. INTRODUCTION

' Previous studies have shown that true! tire noise is affected by

various parameters such as tread design, payment surface, wear,

speed, load, and carcass cgystruction [1-6]— . At the request of the

Office of Noise Abatement,— U. S. Department of Transportation (DOT),

the National Bureau of Standards (NBS) carried out a study to

determine the effects that tire loading, inflation pressure, and

deflection have on truck tire noise generation.

The NBS study was conducted to test the hypothesis that load

effects on tire noise can be disregarded if the inflation pressure is

adjusted according to the load (as specified in the load/ inflation

pressure tables published by the Tire and Rim Association [7]). The

effects of different tire loads were measured in three ways: (1)

varying tire inflation pressure with load according to T&RA

recommendations; (2) constant tire inflation at 75 psi (0.52 MPa); and

(3) constant tire deflection, i.e. constant axle height, maintained by

altering inflation pressure with load.

The work was carried out in two parts. First, a table of axle

height (tire deflection) versus inflation pressure for various load

conditions was developed for a sample of ten tires. This portion of

the study was conducted in the laboratory at NBS, and established the

conditions for the constant deflection portion of the second phase of

the study — the acoustic measurement test program. For the acoustic

measurements two types of bias-ply tires — a typical rib and a typical cross-bar — were tested under nominal loads of 100, 90, 80,

75, and 50 percent of maximum rated load per T&RA recommendations. A

detailed discussion of the two phases of the study and the results

obtained are presented in subsequent sections of this report.

The curg^nt Society of Automotive Engineers Recommended Practice

SAE J57a [8]— — Sound Level of Highway Truck Tires — specifies

standard operating conditions and test procedures for measuring the

noise generated by truck tires. One of the conditions specified by

this recommended practice is the vehicle/ tire loading to be maintained

during the test. SAE J57a specifies that the "...tires shall be

inflated to the maximum pressure and loaded to the maximum load

specified by the Tire and Rim Association for continuous operation at

~ Numbers in brackets refer to the literature references at the

end of this report.

2 / — Now the Office of Heavy Duty Vehicle Research of the National

Highway Traffic Safety Administration.

3/ — The complete text of SAE J57a is reproduced in Appendix A.
highway speeds exceeding 80 km/hr (50 mph)." SAF .T57a allows an exception

to this requirement if the local load limits v/i 11 not permit full rated

load. In this case, "...the test may be conducted at the local load limit

with inflation pressure reduced to provide a tire deflection equal to the

maximum load and inflation pressure, provided the load is not less than 75%

of the maximum rated load." The recommended practice suggests as another

alternative that the tire inflation pressure "...be adjusted to correspond

to the actual load following the appropriate load/pressure tables in the

Tire and Rim Association Yearbook." Thus, SAE J57a permits tests to be

conducted using: (1) maximum rated load and inflation pressure as specified by the T&RA, (2) adjustment of inflation pressure to maintain

constant tire deflection with reduced loading, i.e., constant axle height,

and (3) adjustment of inflation pressure to correspond to the actual load

following T&RA recommendations. All three procedures were evaluated in the

conduct of this study. In addition, measurements were made for the

condition of constant inflation pressure and varying load. This represents

the typical in-service case where the load varies between trips but the

tire inflation pressure is maintained at a constant value.

Data on the interrelated effects of load, inflation pressure, and tire

deflection on tire noise are limited. In past studies in which the effects

of load were investigated [1-5, 9-13], the trend has generally been

consistent that the sound levels increase with increasing tire load. These

studies have shown that, for a constant inflation pressure, increases in

load from 30 to 100 percent of the maximum rated load can have a significant effect on the sound level generated by tires with cross-bar

tread patterns (4-8 dB increase) , while the sound from tires with rib type

tread patterns is relatively unaffected (0-3 dE increase).

Inflation pres-sure also has an effect on tire noise. In the case of

cross-bar tires, a decrease in inflation pressure on the order of 30

percent of the maximum recommended pressure (where the load is kept

constant) generally causes cross-bar tires to be 1-3 dB louder [9-11]. A

similar decrease in the inflation pressure appears to have little effect on

the sound level produced by rib tires; in some cases, there is no change

in sound level [11] and in other instances, there is a slight increase of

about 1 dB [10]

Only one known study reports data on the effect of maintaining a constant tire deflection by reducing the inflation pressure for reduced

tire loads. These data, presented in three different references [3,4,10], are shown in Figure 1 for cross-bar and circumferential rib tires of

bias-plv design. The range between the maximum and minimum noise levels is

2.1 dB for the rib tire and 7.0 dB for the cross-bar tire. Based on these

data it would appear that testing at alternative loads with reduced

inflation pressure would only be valid for loads greater than 75 percent of

the maximum rated T&RA load. Further data to support this conclusion are

presented later in this report.

2
MAXIMUM

A-WEIGHTED

SOUND

LEVEL.

dB

re

20

M

Pa 85

80

75

70

65

60

55

20 40 60 80 100

TIRE LOADING, PERCENT OF MAXIMUM RATED TIRE LOAD

Figure 1. Maximum A-weighted sound level versus tire loading for constant

tire deflection. These data are for coastbys at 50 mph

( 80.5 km/hr) measured using "slow" meter response [10].

3
2. LOAD /INFLATION PRF.SSURF7DFFLF.CTI0N STUDY

Before the acoustical measurement portion of the program was conducted,

it was thought to be desirable to obtain precise information on axle height as

a function of load and inflation pressure. This information would then be

used as the guideline for adjusting inflation pressure when conducting the

acoustical measurements in the field. In addition, these data would also

provide indications of the practical limits of altering inflation pressure

with load in field test situations as specified in SAE J57a and whether the

concept of adjusting inflation pressure to maintain constant tire deflection

is practical, especially for radial truck tires.

4/

A sample of ten truck tires- was tested at NBS to determine the

relationship between these parameters. These truck tires, chosen to represent

a variety of tire types, were all size 10.00-20 or the equivalent tubeless

size 11.00-22.5. The carcass construction and basic tread design of these

tires are listed in Table 1. Contact patch footprints of these tires for a loading of 4760 lb (2159 kg) and an inflation pressure of 75 psi (0.52 MPa)

for the bias-ply tires and 5300 lb (2404 kg) and 95 psi (0.66 MPa) for the

radial tires are shown below this table.

For these tests a series of loads were used in examining the inflation

pressure and deflection characteristics. These loads, listed in Table 2,

correspond to T&RA recommendations for 10.00-20 (or 11.00-22.5) size tires —

with an "F" load rating for the bias-ply tires and a "GM load rating for the

radial tires used in dual applications — for reduced inflation pressures in

5 psi (34.5 KPa) increments from the maximum recommended value at 75 psi

(0.52 MPa) for the bias-ply tires and 95 psi (0.66 MPa) for the radial tires.

It should be noted that T&RA does not recommend inflation pressures for this

size tire below 50 psi (0.34 MPa) for bias-ply tires and 55 psi (0.38 MPa) for

radial tires. To get conditions corresponding to 75 and 50 percent of the

maximum rated tire loads, tests were also conducted at 3570 lb (1619 kg) and

2380 lb (1080 kg) for the bias-ply tires and 3970 lb (1801 kg) [instead of

3975 lb (1803 kg)] and 2650 lb (1202 kg) for the radial tires. The test

procedures for these measurements are discussed below.

2.1. Test Set-Up

These series of tests were performed using a Tinius Olsen-^ universal

testing machine equipped with a def lectometer and an autographic

These tires and the tires used in the acoustic measurement program

were loaned to the government for use in this study by member fleets

of the American Trucking Associations, Inc.

5 / —Commercial test equipment is identified in this report to adequately

describe the test procedures that were utilized. In no case does such

identification imply recommendation or endorsement by the National Bureau of

Standards, nor does it imply that this equipment was necessarily the best

available for the purpose.

4
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Table 1. Construction and basic tread design of tires tested to examine

the relationship between load, inflation pressure and tire

deflection

TIRE

DESIGNATION

CARCASS

CONSTRUCTION BASIC TREAD DESIGN

TUBE TYPE - T

TUBELESS - TL

A bias-ply rib l’L

B bias-ply cross-bar TL

C bias-ply rib T

D bias-ply recap rib TL

E bias-ply cross-bar TL

F bias-ply recap cross-bar TL

G bias-ply recap rib TL

H bias-ply rib T

I radial rib TL

J radial rib TL

B

Contact patch footprints for a loading of 4760 lb (2159 kg) and an inflation pressure of 75 psi (0.52 MPa) for the bias-ply tires

and 5300 lb (2404 kg) and 95 psi (0.66 MPa) for the radial tires.

RADIAL

TIRE B

TIRE J

TIRE D

5
I Table 2. T&RA recommended load and inflation pressure

conditions for 10.00-20 (or 11.00-22.5) size

tires used in dual applications. The biasply tires are load range "F" and the radial

tires load range "G".

Load $ lb*

Inflation Pressure, psi**

Bias-Ply

Load Range "F"

Radial

Load Range "G"

5300 X 95

5120 X 90

4950 X 85 ’

4760 75 80

4580 70 75

4380 65 70

4180 60 65

3970 55 60

3760 50 55

3570 4 50 X

2650 X 55

2380 50 X

X = No test conducted at this load

* To convert the load in pounds to kilograms divide by

2.2046 lb/kg.

** To convert psi to Pascals multiply by 6894.8 Pa/psi.

load-deflection recorder. The testing machine was calibrated according to

American Society for Testing and Materials (ASTM) Standard E4-72, Standard

Methods of Verification of Testing Machines [14]. Figure 2 shows the testing

machine with a tire mounted on an axle and suspended above the floor. In this

configuration only the upper portion of the tire is deflected.

6
fc -sc* ' . >! ti

TESTING MACHINE

CROSSHEAD

CONTROL

PANEL

TEST TIRE

(Suspended above floor)

j*t»«-'i £ jin

Figure 2. Tinius Olsen universal testing machine with tire mounted for testing

7
The tire load was applied to the top of the tire by lowering the loading

plate attached to the crosshead of the testing machine. This load was measured using a lever arm-LVDT system and read from the large dial indicator

on the control panel. This reading is accurate, to within + 1 percent of the

actual load. The crosshead travel of the testing, machine was measured with an accuracy of + 0.054 in. (+ 1.372 mm) using, the deflectometer attachment

mounted as .shown in Figure 3. For these tests the crosshead was lowered to

apnly a small load —less than 10 lh (4.54 kg) —to the tire to ensure contact

with the loading nlate. This position was assumed to represent zero deflection. The tire was then loaded by further lowering of the crosshead at

a speed of 1.5 in. /min (0.635 mm/s). When the appropriate load was attained,

the crosshead motion was stopped and the tire deflection read from the

deflectometer. Figure 4 shows a load applied to a tire and the resultant tire

deflection

For these tests the tire inflation pressure was measured using a spring

loaded sliding scale pressure gauge. This particular gauge was chosen so that

the same pressure gauge could be used both in the lab and in the field during

the acoustic test program. This gauge was checked against calibration

standards at MBS and was accurate within + 1 psi (+ 6.9 KPa) for the range of

pressures from 20 to 100 psi (0.14 to 0.69 KPa) at 70°F (21°C).

2.2 Test prooedures/Re.sults

a. Varying Load and Inflation Pressure - T&RA

In this test, the tire was inflated to the T&PA recommended pressure and

mounted on the testing, machine. A compressive load was gradually applied

until reaching the maximum rated load for the test inflation pressure at

which point the deflection was measured. The load was then removed, the

inflation pressure adjusted and the load re-applied. ^he process was repeated

for each combination of load and inflation pressure. The results are shown in

Table 3.

b. Constant Inflation

The test tire was inflated to 75 psi (0.52 MPa) for the bias-ply tires

and 95 psi (0.66 MPa) for the radial tires and maintained at these pressures

throughout the test. A sequence of compressive loads were applied to the

tire, and the resulting deflection was recorded for each loading condition.

The results are shown in Table 4.

c. Constant Deflection

The maximum rated T&RA loads and inflation pressures were chosen as the

reference conditions for maintaining constant deflection. These conditions

are 4760 lb (2159 kg) and 75 psi (0.52 MPa) for the bias-ply tires and 5300 lb

(2404 kg) and 95 psi (0.66 MPa) for the radial tires. In this test the tire

8
Figure 3. Tire with load being applied showing the def lectometer attachment.

9
"T^rr

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« v Jr

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’ “ V / * 1 ¥ ry< i

Figure 4. Universal testing machine applying a load to a tire and the resulting

tire deflection.

10
Table 3. Measured deflection of a sample of ten truck tires for a combination of load and inflation pressures based on T&RA

recommendations. The means and standard deviations are

for the upper test conditions.

TIRE DESIGNATION

Load

lb

(kg)

Inflation A B C D E F C. H 1+ .!+

psi (MPa) Tire Deflection, inches*

5300

(2404)

90

(0.62)

X X X X X X X X 1.43 1.46

5120

(2322)

85

(0.59)

X X X X X X X X 1.43 1.49

4950

(2245)

80

(0.55)

X X X X X X X X 1.46 1.52

4760

(2159)

75 (0.52)

1.19 1.09 1.18 1.14 1.15 1.18 1.17 1.22 1.47 1.52

4580

(2077)

70

(0.48)

1.20 1.08 1.13 1.13 1.12 1.14 1.12 1.19 1.47 1.52

4380

(1987)

65

(0.45)

1.14 1.05 1.13 1.13 1.11 1.10 1.14 1.20 1.48 1.55

4180

(1896)

60

(0.41)

1.18 1.06 1.12 1.17 1.12 1.05 1.08 1.19 1.50 1.53

3970

(1801)

55 (%38)

1.14 1.07 1.12 1.12 1.13 1.02 1.17 1.16 1.51 1.55

3760

(1706)

50

(0.34)

i . 15 1.06 1.12 1.13 1.13 0.99 1.14 1.18 1.51 1.54

Mean 1.17 1.07 1.13 1.14 1.13 1.08 1.14 1.19 1.47 1.50

Standard Deviation 0.03 0.01 0.02 0.02 0.01 0.07 0.03 0.02 0.03 0.03

3570

(1619)

50

(0.34)

1.17 1.00 1.07 1.05 0.98 0.94 1.08 1.15 X X

2650

(1202)

50

(0.34)

X X X X X X X X 1.18 1.10

2380

(1080)

50

(0.34)

0.89 0.67 0.77 0.80 0.79 0.60 0.77 0.85 X X

X - No test conducted at this load.

*To minimize the number of values shown in this table, the results are given only

in inches. To convert to centimeters multiply by 2.54 cm/ in.

+Tests were conducted using the inflation pressures recommended for radial tires

which are 5 psi (34.5 KPa) higher for similar loads.

11
Tabic 4. Measured deflection of a sample of ton truck tires for eight

different loading conditions at a constant Inflation pressure

of 75 psi (0.52 MPa) for bias-ply tires and 95 psi (0.66 MPa)

for radial tires. Deflection rate estimated using linear

regression curve fitting.

TIRE DESIGNATION

Load,

lb

(kg)

A B C D E F G H I J

Tire Deflection, inches*

5300

(2404)

X X X X X X X X 1.43 1.46

5120

(2322)

X X X X X X X X 1.40 1.47

4950

(2245)

X X X X X X X X 1.37 1.44

4760

(2159)

1.19 1.09 1.18 1.14 1.15 1.18 1.17 1.22 1.33 1.40

4580

(2077)

1.14 1.05 1.15 1.11 1.11 1.15 1.13 1.17 1.30 1.36

41380 (1987)

1.12 1.01 1.12 1.06 1.07 1.13 1.10 1.13 1.26 1.32

4180

(1896)

1.10 0.98 1.08 1.02 1.04 1.11 1.05 1.09 1.22 1.28

3970

(1801) 4

1.05 0.95 1.04 0.98 1.00 1.13 1.02 1.06 1.17 1.23

3760

(1706)

1.01 0.93 1.01 0.95 0.96 1.11 0.98 1.03 1.13 1.20

3570

(1619)

0.98 0.89 0.98 0.90 0.92 1.09 0.95 0.99 X X

2650

(1202)

X X X X X X X X 0.89 0.97

2380

(1080)

0.85 0.65 0.75 0.68 0.78 0.69 0.91 0.64 X X

Deflection Rate,

inches per 1000

pounds load

0.14 0.18 0.18 0.19 0.16 0.19 0.11 0.24 0.20 0.20

X - No test conducted at this load.

* To minimize the number of values shown in this table, the results are given

only in inches. To convert to centimeters multiply by 2.54 cm/in.

12
was inflated to the maximum rated T&RA inflation pressure and mounted on the

testing machine. A compressive load corresponding to the maximum rated T&RA

load was applied to the tire and the deflection was measured. This deflection

was used as the reference value for maintaining constant tire deflection for

the other test loads. As the load was reduced to the other load conditions,

the tire inflation pressure was reduced to maintain constant deflection. The

results of this test are given in Table 5.

d. Tire Footprints

In addition to the deflection and inflation pressure measurements, tire

footprints were made for several of the load and inflation pressure

conditions. Printing ink was applied to the surface of the tire in the

contact region and a sheet of recording paper was placed on the loading

surface of the testing machine. Compressive loads were applied to the tire

and an inked print (footprint) of the contact area of the tire was obtained.

Footprints of tire C for several load and inflation pressure conditions are shown in Figure 5.

2.3 Discussion of Test Results

a. Varying Load and Inflation Pressure — T&RA

The data given in Table 3 indicate that in general the tire deflection is

approximately constant for the range of loads and inflation pressures

recommended in the T&RA tables. This is shown by the narrow range of standard

deviations listed in the lower portion of Table 3. Also listed in this table

are the mean values for the T&RA recommended load and inflation pressure

conditions. For this range of loads, the mean deflections for the bias-ply

tires range from 1.07 to 1.19 in. (2.72 to 3.02 cm) with a range of standard

deviations from 0.01 to 0.07 in. (0.03 to 0.18 cm). For the two radial tires

tested, the mean deflections are larger than for the bias-ply tires — 1.47

and 1.50 in. (3.73 and 3.81 cm) for tires I and J, respectively. Although

larger, the deflection for the two radial tires is still approximately

constant for the range of loads tested. Thus, the SAE J57a alternatives of

adjusting the inflation pressure according to the T&RA tables can be assumed

to give approximately constant tire deflection for loads greater than 75 to 80

percent of the maximum rated load.

The variations which were measured can be easily understood when one considers that the T&RA load/inflation pressure tables are generated using an empirical equation — designed to provide constant tire deflection — that expresses tire load as a function of inflation pressure, tire and

rim dimensional characteristics and an appropriate load factor based on the

general type of tire construction and usage (single or dual) [15]. This

13
Table 5. Measured inflation pressure required to maintain constant tire

deflection under different loading conditions for a sample of ten truck

tires. The mean and standard deviations are for the eight hias-ply

test tires.

TIRE DESIGNATION

Bias-Ply Reference B L D H I J Tires Only Deflect Ion*

in. (cm) 1.19

(3.02)

1 .09 (2.77) 1.18

(3.00)

1.14

(2.90) 1.15

(2.92) 1.18

(3.00)

1.17

(2.97)

1.22 (3.10)

1.43

(3.63)

t .46 (3.71) Mean

(Standard

Deviation)

Bias-Ply Radial

Load

lb (kg) Tire Inflation Pressure, psi**

5300

(2404)

X X X X X X X X 95 95 X 90 95

5120

(2322)

X X X X X X X X 92 93 X 85 90

4950

(2245)

X X X X X X X X 89 90 X 80 85

4760

(2159)

75 75 75 75 75 75 75 75 86 86 75 75 80

4580

(2077)

71 71 72 70 72 .71 72 71 82 82 71.3

(0.7)

70 75

4380

(1987)

68 68 68 68 68 69 69 68 79 79 68.3

(0.5)

65 70

4180

(1896) 63 64 4f

3 64 64 64 65 64 75 76 63.9

(0.6)

60 65

3970

(1801)

59 59 60 60 60 60 61 60 70 71 59.9

(0.6)

55 60

3760

(1706)

55 55 55 56 58 56 57 57 66 66 56.1

(1.1)

50 55

3570

(1619)

51 51 52 52 50 53 53 53 X X 51.9

(1.1)

50 55

2650

(1202)

X X X X X X X X 43 43 X 50 55

2380

(1080)

29 29 30 30 31 31 30 31 X X 30.1

(0.8)

50 55

X - No Test conducted at this load.

6 Reference deflection' corresponds to deflection at maximum rated load and inflation pressure:

4760 lb (2159 kg) and 75 ps 1 (0.52 MPa) for the bias-ply tires and 5300 lb (2404 kg) and 95 psi (0.66 MPa) for

the radial tires.

** To minimize the number of values shown in this table, the results are given only in psi.

To convert to Pascals multiply by 6894.8 Pa/psi.

14
(a) 4760 lb (2159 kg), 75 psi (0.52 MPa)

(b) 3570 lb (1619 kg), 50 psi (0.34 MPa)

(c) 2380 lb (1080 kg), 50 psi (0.34 MPa)

Figure 5. Footprints of tire C (bias-ply rib) for various load and

inflation pressure conditions based on T&RA recommendations.

15
equation is applied to a wide variety of tire types produced by the

different manufacturers. Thus, it is not surprising that there are slight

variations of the actual measured deflections using the T&RA tables.

b„ Constant Inflation

As expected, tire deflection Increases with tire load. The constant

Inflation pressure data given in Table 4 show that the Increase of

deflection with load, or deflection rate, is approximated constant over the

load range of Interest. The linear regression curve fit indicates an increase of deflection with load ranging from 0.11 to 0.24 in. per 1000 lb

load (0.28 to 0.70 cm per 453.6 kg). The deflection rate is slightly larger

for the two radial tires than for most of the bias-ply tires — an average

value o f 0.20 versus 0.17 in. per 1000 lb (0.51 versus 0.44 cm per 453.6 kg)

for radial versus bias-ply. Other comparisons -- new versus recap bias-ply

and new rib versus new cross-bar bias-ply — show little difference in the

deflection rate based on the averages for these groupings.

c. Constant Deflection

In general, the inflation pressures required to maintain constant tire

deflection shown in Table 5 do not agree with the corresponding T&RA

recommendations. The measured inflation pressures are greater than those

recommended by T&RA with the difference between the average and T&RA values

increasing from the pre-established value of zero at the maximum recommended

conditions to over 6 psi (41.4 KPa) for the bias-ply tires and 11 psi

(75.8 KPa) for the radial tires at 3760 lb (1706 kg). As mentioned in the

discussion of Section 2.3a, the T&RA load/ inf lation pressure tables are derived from an empirical load equation designed to provide constant tire

deflection. Since this equation is applied to a ivide variety of tire types,

it is not surprising, that there are variations between the recommended and

measured inflation pressures.

Another possible explanation for the higher inflation pressures

pertains to the techniques used in conducting this portion of the test.

For the T&RA deflection measurements (Table 3), -the load was removed

between the different load settings, while for the constant deflection

measurements (Table 5), it was not. As a consequence of not removing the

load, the friction between the tire and loading plate prevented the tire

footprint from reconforming. As a result, the tire deflections were larger

for the same load conditions. For example, consider tire C at a load of

4380 lb (1987 kg). From Table 3, the inflation pressure and deflection

are 65 psi (0.45 MPa) and 1.13 in. (2.87 cm), respectively, whereas from

Table 5 they are 68 psi (0.47 MPa) and 1.18 in. (3.00 cm). Thus, rather than

a lower inflation pressure for a larger deflection as would be expected, the

inflation pressure is higher. The mechanism which causes this to occur is

illustrated in Figure 6. When the load is removed, the inflation pressure

decreased and a smaller load reapplied to the tire, points A and B change to

the positions shown on the right. If the load is not removed, points A and

16
INFLATION PRESSURE DECREASED

SMALLER LOAD REAPPLIED

Figure 6. Sketch of tire cross section illustrating the mechanism causing

the constant deflection tire inflation pressures to be higher

than the T&RA recommended values.

17
B tend to stay in contact with the loading surface because of friction. As a result, hig^r inflation pressures are required to maintain the same deflection.—

Even if these variations do exist, this is not necessarily a problem.

Although a strict comparison of the data shown in Tables 3 and 5 cannot be

made because of the differences in the test procedures discussed above, these

data indicate that relatively large changes in inflation pressure on the order

of 3 to 5 psi (20.7 to 34.5 KPa) result in relatively small changes in tire

deflection on the order of 0.02 to 0.05 in. (0.05 to 0.13 cm). Thus, even though adjusting the inflation pressure according to T&RA recommendations

might not truly provide constant tire deflection, the variation of tire

deflection from that at the maximum recommended conditions would be relatively

small. This would be acceptable provided that the tire sound levels are not

significantly affected by these small changes of tire deflection. Also, this

would indicate that adjustment of the inflation pressure within + 2 psi

(+ 13.8 KPa) would be adequate. This tolerance would greatly simplify setting

up the proper test conditions when conducting measurements in the field.

d. Tire Footprints

Tire footprints, such as those shown in Figure 5, were obtained for the

load and inflation pressure conditions listed in Table 6. In this table the

gross contact areas — the area inside the perimeter of the contact patch

including the open tread elements — are given for each of these footprints.

These gross contact areas were measured using a rolling disk planimeter.

The tire footprints shown in Figure 5 correspond to 100, 75 and 50

percent of the maximum rated load with T&RA recommended inflation pressures of

75, 50 and 50 psi (0.52, 0.34 and 0.34 MPa), respectively. The first two load

and inflation pressure conditions give approximately the same tire deflection

and as shown by the data in Tab^e 6 approximately thg same overall contact

patch area -— 65.8 and 64.7 in. (424.5 and 417.4 cm ). Reduction of the load

to 2380 lb (1080 kg) while holding the inflation pressure at 50 psi (0.34 MPa)

results in a much smaller tir£ deflectio^ and a corresponding decrease in the

gross contact area to 52.4 in (338.1 cm ).

—^This hypothesis was suggested by Dr. George R. Thurman formerly of the

Firestone Tire and Rubber Company (retired) [16]. Dr. Thurman had noticed

similar discrepancies when conducting deflection measurements and found

that if the tire/loading plate interface was lubricated, these differences

were for all practical purposes eliminated. Since this was suggested

after the tests had been completed and the tires returned, this hypothesis

could not be verified.

18
Table 6. Gross contact areas for various load and inflation pressure

conditions

LOAD, INFLATION TIRE DESIGNATION TEST

lb PRESSURE. A B 1' E r U 1+ J+ CONDITION

(kg) ps 1 ^MPn) GROSS CONTACT PATCH AREAsquare inches *

5300

(2404)

90

(0.62)

X X X X X X X X 73.7 69.0

4760

(2159)

75 (0.52)79.5 67.3 65.8 70.7 69.5 71.4 69.7 74.9 73.4 70.9

3970

(1801)

55 (0.38)X X X X X X X X 74.6 72.4 T&RA

3570

(1619)

50

(0.34) 75.3 65.9 64.7 66.2 68.6 69.9 65.7 72.1 X X

2650

(1202)

50 (0.34)

X X X X X X X X 58.1 56.5

2 380 (1080)

50 (0.34)

55.7 49.1 52.4 50.8 50.9 55.6 51.4 55.0 X X

4760

(2159)

4180

(1896)

3570

(1619)

2 380 (1080)

75 (0.52)

63 (0.41)

52 (0.36)

30

( 0 . 21 )

65.8

65.2

61.9

59.2

CONSTANT DEFLECTION

5300

''2404)

5120

(2322)

4760

(2159)

4380

(1987)

4180

(1896)

3970

(1801)

3570

(1619)

2650

'' 1202 )

2380

(1080)

Tire C

75 (0.52)

75 K0. 52)

75 0.52)

75 (0.52)

Tire I

( 0 . 66 )

9 5

( 0 . 66 )

95

( 0 . 66 )

95

( 0 . 66 )

95

( 0 . 66 )

95

( 0 . 66 )

65.8

63.5

57.4

43.6

73.7

71.4

67.4

64.7

59.9

46.1

CONSTANT INFLATION

X - No test conducted at this load.

*To minimize the number of values shown in the table, the results are given only in square inches. To convert to square centimeters multiply by 6.45 cm^/in

+T4RA tests were conducted using the Inflation pressures recommended for radial tires which are 5 psi (34.5 KPn) higher for similar loads.

19
For constant tire deflection the p,ross contact area decreases slightly

for the two smaller loads, but it is

2 ^asentiall

£ constant — within + 6

percent of the mean value of 63.0 In (406.6 cm ). This agrees with the

results presented in reference [17] which indicate that if inflation pressure

and load are simultaneously varied to maintain constant tire deflection, the

contact area of the tire will remain effectively constant. [It should be

noted that when the tire footprints are made the load is removed so that a piece of recording paper can be placed between the loading plate and tire.

Thus, the problem of tire adhesion to the loading plate affecting the

footprint, as illustrated in Figure 6, is not a problem.]

For constant inflation pressure and varying load, the gross contact area

for tire^C (bias-ply rib) decreases linearly with decreasing load-from

65.8 in. (424.5 cm ) at 4760 lb (2159 kg) to 43.6 in. (281.3 cm ) at 2380 lb

(1080 kg). Based o^ linear regression curve fitting, this decrease is

approximately 10 in. per 1000 lb load (64.5 cm per 453.6 kg). The same is

also true for Tire I (radial rib^where the gross contact ar^a linearly

decreased by approximately 10 In. per 1000 lb load (64.5 cm per 453.6 kg).

The objective of this portion of the program was to investigate the

relationship between load, inflation pressure and tire deflection for a sample

of truck tires. The significance of these data depends upon how the measured

sound levels vary with these parameters. The acoustic data are presented in

the next section.

3. ACOUSTICAL MEASUREMENT PROGRAM

The operational procedures and measurement /analysis instrumentation

utilized In this load/deflection study were similar to that used in previous

DOT/NBS truck tire noise studies. Data were obtained for a set of rib and of

cross-bar tires of bias-ply design — tires A and B of Table 1, respectively.

The test procedure utilized was essentially identical to that specified

in SAE J57a; however, the following exceptions should be noted:

"Fast" meter response was utilized.

The hard surface (vehicle path and measurement area) was sealed

asphalt

The distance between the point of entrance and point of exit of the

test section was 600 feet (182.9 m)

O Mud flaps were left on the vehicle during testing.

20
Detailed descriptions are provided of the vehicle configurations, test

tires, the field test site utilized Cor data acquisition and the

operational test procedure in Appendix R.

3.1 Acoustical Measurement Results

Measurements were made for test runs with the load and inflation

pressure conditions shown in Table 7. To reduce the total number of test

runs, fewer load conditions were tested than were discussed in Section 2.

The inflation pressure data shown for the constant deflection conditions

are the values given in Table 5 for tires A and B. For these tests the

inflation pressures were set to the desired value and the vehicle run for a minimum of ten miles to allow the tires to warm up. The vehicle was then

stopped and the inflation pressures were again adjusted to the desired

value. Immediately following this, the acoustic measurement test runs were

made. A minimum of two test runs were made for each of these conditions.

The data for these test runs, which consisted of the maximum

A-weighted sound level for each coastby, are presented in Tables 8 and 9 for tires A and B, respectively. The data for each run are adjusted to

50 mph (80.5 km/hr) using a 40 log V relationship between sound level and

vehicle speed [18] and then averaged for each test condition.

The data for the conditions of constant tire deflection and T&RA

recommended inflation pressure are plotted in Figure 7 as the maximum

A-weighted sound level versus tire load in terms of percent of maximum

rated tire load. As can be seen in Figure 7, the results obtained

following the T&RA recommendations are quite similar to those obtained by

maintaining constant tire deflection for both types of tire. For the rib

tire (tire A), the test results at the alternate load/ inflation pressure

conditions are within +0.5 dB of the sound level at maximum rated load and

inflation pressure for loads greater than 75 percent, indicating little

sensitivity to load or inflation pressure. For the cross-bar tire (tire B)

the data are within + 1.5 dB of the sound level at maximum rated load and

inflation pressure. Thus, both alternative loading procedures can introduce variations relative to the values at the maximum rated load and

inflation pressure.

As an alternative to adjusting the inflation pressure to correspond

to either T&RA recommendations or constant tire deflection, measurements

were made for constant inflation pressure and varying load. These data are plotted in Figure 8. The variations of the sound levels from the values at

the maximum rated load and inflation pressure are +0.2 to -0.3 dB for tire

A and 0 to -0.7 dB for tire B for loads greater than 70 to 75 percent of

the maximum rated load. These variations are less than those observed for

similar loading when the inflation pressures were adjusted. Thus it

appears that based on this set of data, if reduced loading is necessary to

21
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22
Table

8.

Maximum

A-weighted

sound

levels,

as

measured

at

50

feet

(15.2

m),

for

coastbys

ata

nominal

speed

of

50

mph

(80.5

km/hr)

over

an

asphalt

surface

for

tire A

(bias-ply

rib

tire).

These

data

are

adjusted

to

exactly

50

mph

(80.5

km/hr)

using a

40

log V

relationship

between

soun

level

and

vehicle

speed

and

then

averaged

for

the

two

test

runs.

”t3 2o « 2 ^ So

C/» ssu — o§0m co o a.

43 Cl 4J JZ o ao ph 0 4) JK k- 1 < CO

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aIf

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Average jf

runs PH

nt

sT

st

O

74.5

u

x: .r: -3 o.' - 2 0

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m

<r sr

m

O

in

fs

00

p-»

PH

Tt

m

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ST

T3VU3O sT

PH

r»

CMvr

nO

r-T

Om

CO

rO

rs

PH

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st

CM>T

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Vehicle Speed mph

(km/hr)

m

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m o o in oo

O'

O' co <r fr. rH PH in oo

in

O o m oo

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CONSTANT

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TJ§o

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ua £ i > V5 s^

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m o o m coin

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sr rs 0 V —< U y-v u 3 -< 83

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TIRE &

RIM

ASSOCIATION

RECOMMENDATIONS

T3§0

COTT CL. 43 _1 -c o

cO pj

43 43 X U 1 -3 n3 “ n — —' 41 X >

ifl 4) T. -1

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23
V3

(1074) 2368 (1622) 3576 (1795) 3958 (1985) 4376 (2174) 4793

LOAD

PER

TIRE

lb (kg)

ro - N> - - - ro - NO - TEST RUN

NUMBER

so

(0.34) 50 (0.34) 55 (0.38) ? O'

X' u' cn

(0.52) 75

Inf

iat

ion

Pressure psl (KPa)

TIRE

4

RIM

ASSOCIATION

RECOMMENDATIONS

50

(80.5) 50(80.5) 49(78.9)

'-J X-'

OJ

'-J XGO vO

VD

49

(78.9) 49

(78.9) 49(78.9) co v-n O O 50

(30.5)

Vehicle mph Speed

(ka/hr)

79.4 80.2 82.4 CDO

X'

79.2 79.6 79.0 73.6 80.0 80.8

Measured

t- x

a a, < X a *— »- 3

- c

a.

CD >•

• ^ z:

n> n> 0

(~r

rr

1

’ ft -a c~

u» CDo

cD

CL

X80.2 COCD

CD

79.6 80.0

''J

n£3 X»

79.0 80.0 80.8

o o cl V V c O Vi X* rr Bare \t) c_

zr zr n

79.8 82.0 79.8 79.2 CDO

X*

Average

of

runs

(0.20) 29 51

(0.35) ?u.

js'0 (46‘0) 99 o

c/I 'O' to

Inflat

ion

Pressure psi

(MPa)

CONSTANT

DEFLECTION

"V XCO CO'•J XCD

U1

**J X*- CD vO vO

48

(77.3) CO U1 o o

cn

-J X-

-V CD

CO

50

(80.5) 50(80.5) 50

(80.5) 50(60.5) Vehic

le

mph Speed

(km/hr)

CDO 78.0 81.0 81.4 CD

)—

N>

vX>

79.0 79.4 o

o

CDo

CO Measured

Maximum

A-Weighted

Sound

Level,

d3

re

20

uPa

81.1 78.7 81.4 82.1 81.2 79.9 79.0 vOX*

OOO

O

CDO

CO

CD rr > o o c- vi Vi C O V) Fb s

^•o &.

a* cr

79.9 81.8 81.1 79.2 80.4 Average

of

runs

50

(80.5) 52

(83.7) 51(82.1) X'

CD vO

sD

50

(80.5) X> CD *£> 50

(80.5) CD vO

vO

50

(80.5) 50

(80.5)

Vehicle mph Speed (kn/hr)

CONSTANT

INFLATION

[75

psl

(0.52

MPa)]

78.8 v£>

CT'

79.4 79.8 80.0 CDO

X»

80.0 79.0 80.0 80.3

Measured

r- X

a cu < X

»- U

§ & >

m »:

n, ft» IV OL O cr

Id t

ftt CDo

§

a.

lT» a> 5 o s

CDO

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noo

o

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. J

80.8

o O U. VI VI c o (a 1-8 S.

cr zr H

78.8 \£>

CT' o

x>

sO

CDo

x>

Average

of

runs

Table

9.

Maximum

A-weighted

sound

levels,

as

measured

at

50

feet

(15.2

m)

,

for

coastbys

ata

nominal

speed

of

50

mph

(80.5

km/hr)

over

an

asphalt

surface

for

tire B

(bias-ply

cross-bar

tire).

These

data

are

adjusted

to

exactly

50

mph

(80.5

km/hr)

using

a

40

log V

relationship

between

sound

level

and

vehicle

speed

and

then

averaged

for

the

two

test

runs.
85

CO Q.

4. o

CM

0>

00

>tu

__l o

o

CO

T & RA RECOMMENDATIONS — CONSTANT DEFLECTION

C

ULI £I <

2

x

<

2

80

75

70

65

TIRE B W

TIRE A

-o10 20 30 40 50 60 70 80 90 100

TIRE LOADING. PERCENT OF MAXIMUM RATED TIRE LOAD

Figure 7. Maximum A-weighted sound levels, as measured at 50 feet (15.2m),

versus tire load for various inflation pressures. These data

correspond to vehicle coastbys at 50 mph (80.5 km/hr) on an asphalt surface.

25
0 10 20 30 40 50 60 70 80 90 100

TIRE LOADING. PERCENT OF MAXIMUM RATED TIRE LOAD

Figure 8. Maximum A-weighted sound levels, as measured at 50 feet (15.2 m)

versus tire load for constant inflation pressure. These data

correspond to vehicle coastbys at 50 mph (80.5 km/hr) on an asphalt surface.

26
comply with local load limits, testing can be performed using the

maximum Inflation pressure without encountering serious errors,

provided that the loads are greater than 70 to 75 percent of the

maximum rated tire load. This would be more convenient and practical

since this essentially represents the typical in-service case where

the load varies between trips but the tire inflation pressure is

maintained at a constant value.

3.2 Conclusions

Based on the data presented in this report the following

conclusions can be made:

For tire loads greater than 70 to 75 percent of the maximum rated

loads, smaller variations of the measured sound level were

observed when maintaining constant inflation pressure than when

adjusting the inflation pressure to correspond to either T&RA

recommendations or constant tire deflection.

The load/inflation pressure adjustments recommended in SAE J57a — constant tire deflection and T&FA recommendations — induced

variations in the resulting sound level from those at the maximum

rated load and inflation pressure on the order of +0.5 dB for the

bias-ply rib tire and +1.5 dB for the bias-ply cross-bar tire

which were tested. Thus, use of these alternative loading

conditions can introduce variations relative to the values at the

maximum rated load and inflation pressure.

The T&RA tables give load and inflation pressure combinations

which give approximately constant tire deflection.

Tire deflection is relatively insensitive to small changes of

inflation pressure. Changes in inflation pressure from 3 to 5 psi (20.7 to 34.5 KPa) produce changes in tire deflection on the

order of 0.02 to 0.05 in. (0.51 to 1.27 mm).

27
4. APPENDIX A. SAE RECOMMENDED PRACTICE FOR MEASUREMENT OF TRUCK TIRE NOISE"'

SOUND LEVEL OF HIGHWAY

TRUCK TIRES—SAE J 57a SAE R«comm«nd*d Practice

/. Introduction —Thu SAE Recommended Practice establishes a test pro- cedure for measuring the sound level produced by tire* intended primarily for. highway uv on motor trucks, truck tractors., trailers and semitrailers, and

buses. The procedure provides for the measurement of the sound generated by

a set of test tires, mounted on the rear axle operated at 80 km/h (50 mph) and

at maximum rated tire load. Specifications for the instrumentation, the test site, and the operation of the

test vehicle are set forth to minimize the effects of extraneous sound sources and to define the bajis of reported sound levels. Factors influencing sound level measurement and reference to sound levels are given in the Appendix.

2. Instrumentation —The following instrumentation shall be used for the measurements as required

2.1

A sound level meter which satisfies the Type 1 requirements of American National Standard Specification for Sound Level Meters. SI 4-1 ^7

2.1

I As an alternative to making direct measurements using a sound level meter, a microphone or sound level meter may be used with a magnetic tape

recorder and/or a graphic level recorder or other indicating instrument, providing the system meets the requirements of SAE J

1 84 , Qualifying a Sound Data Acquisition System, with slow response specified in place of fast response as applicable to paragraph 1.6 therein. 0 2.2 An acoustical calibrator, having an accuracy of ±0.5 dB, for establishing the calibration of the sound level meter and associated instrumentation

2.3 An anemometer having an accuracy of ± 10% at 19 km/h ( 12 mph)

3. Teat SiU

3.1 The test site shall be located on a flat area which is free of reflecting surfaces (other than the ground), such as parked vehicles, trees, or buildings within 30 m (100 ft) of the measurement area. 3.2 The vehicle path shall be relatively smooth, semipolished, drv, Port- land cement concrete which is free of extraneous surface material.

3.3 The microphone shall be located 15 m (50 ft) from the centerline of the vehicle path at a height of 1.2 m (4 ft) above the ground plane The

normal to the vehicle path from the microphone shall establish the micro- phone point on the vehicle path. See Fig 1. 3.4 The test zone extends 15 m (50 ft) on either side of the microphone

point along the vehicle path. The measurement area is the triangular area formed by the point of entrance into the test zone, point of exit from the test zone, and the microphone.

3.5 The measurement area should be surfaced with concrete, asphalt, or similar hard materia! and. in any event, shall be free of snow, grass, soil, ashes, or other sound-absorbing materials. 3.6 The ambient sound level (including wind effects) at the test site shall be at least 10 dB below the level of the test vehicle operated in accordance

with the test procedure

3.7 The wind speed in the measurement area shall be less than 19 km h (12 mph).

Rrpnri it \ rhM Ir S«mnH I /vrl ( Vwnintlifr • |>|Krrvrd July I1M and Iasi frvurd June I*l7b Approved by Ameri* an Nihimal .Sundiuti Intnimr November |1?h KaiionaU- Siairment Available *

FIG. 1—TEST SITE (SEE PARAGRAPH 3). (VEHICLE MAY BE RUN IN EITHER DIRECTION)

— Reprinted with permission from 1978 SAE Handbook (c) 1978 Society of

Automotive Engineers, Inc.

28
4. Seat Vehicle

4.1 The vehicle shall hr a motor trui k equipped with two ailn (*» nonp<iwered steering axle and a powered axlri 4.2 The vehicle shall h«vr a platform, rack, or van bitdy < apahlr of

retaining the loading or ballast I his body shall have an essentially Hal ami

horizontal undersurface, and b*- mounted such that this suriai e lias a 230 ± 100 mm (9 f. 4 in) clearance with the lire fully loaded This body shall be nominally 2440 mm (96 in; in width and extend a minimum of ‘HO mm

(36 in) rearward of the rear (powered) axle irnlerline

4.3 Mud flaps should he removed at the test site, if permissible

5. Tires

5.1 Tires used for dual installations shall be dual mounted (four tires) on

the rear axle for testing Tires used in single installations (wide base) shall lx- mounted singly A lire used as both duals and singles may require test at both

dual and single mounting I he sound level reported must be identified as to type of mounting

5.2 The tires shall be inflated to the maximum pressure and loaded to the maximum load spe< ified by the I ire and Kim Association lor continuous

operation at highway speeds exceeding 80 km/h (50 mph)

5.2

I If local load limits will not permit full rated load, the test may be conducted at the local load limit with inflation pressure reduced to provide a

tire deflection equal to the maximum load and inflation pressure, provided the load is not less than 75% of the maximum rated load As an alternative, the pressure in the tires can be adjusted to correspond to p

the actual load following the appropriate load/ pressure tables in the l ire and Rim Association Yearbook Because the » hour of procedure may cause small

differences in level, such levels shall not be reported unless they are identified with the percent load used

5.3 Quiet tires are recommended for use on the front axle.

6. Procedure

6.1 The test vehicle shall be operated in such a manner (duch as coasting)

that the sound level due to the engine and other mechanical sources is minimized throughout the test zone The vehicle spiced at the microphone

point shall be 80 km/h (50 mph).

6.2 The sound level meter shall be set for slow dynamic response and the A-weighting network The observer shall record the highest level attained during each pass of the test vehicle, excluding readings where known acoustical interferences have occurred

6 2 1 Alternatively, each pass of the test vehicle may be recorded on magnetic tape and subsequently analyzed with a sound level meter and/or graphic

Irvel recorder i 6.3 There shall be at legist thrre measurements The number of measure- ments shall equal or exceed the range in decibel* of the levels obtained

6.4 The sound level reported shall be the average of the two highest readings which arr within 2 dB of each other 7. General Comments

7.1 It is recommended that technically competent personnel select the equipment to be used for thr test measurements and that these tests be conducted only by persons familiar with the current techniques of sound measurement

7.2 All instrumentation should be operated according to the practices recommended in the operating manuals or other literature provided by the manufacturer All stated precautions should be observed Some specific items

for consideration are

7 2 1 Specifications for orientation of the microphone relative to thr ground

plane and the source of sound should be adhered to (Assume that the sound

source is located at the microphone pxxnt )

7 2 2 Proper signal level*, terminating un|x-dam-e>. and cable lengths should lie maintained on all multi instrument ineaMiirment nstfms

7.2.3 The ellr» i of extension cables ami otho »oiH|v»nrnt' should hr taken

into account in the talihralmn pmcrdutr

7 2 I The position ol the observer relative to the nut tophonr should lx- a\ recommended

7.3 Instrument m.mufat hirer’s recommended calibration procedure and

si hedule for individual instruments should lx- employed Field calibrations should be made immediately before and alter tcsiiug rath set ol tires 7.4 Not more than one person, other than the observei reading the meter, shall he within 15 m (50 It) of the vehicle path oi the microphone, and

that person shall Ik- directly behind the observer reading the meter, on a line through the microphone and the observer

7.5 The sound level of the tires being tested is valid only when the sound

level of the vehicle rquippx-d with quiet tires is at least 10 dB below that of the vehicle equipped with test tires. The sound levels obtained with this proce- dure may be used for a relative ranking of the test tires, if the sound level of

the vehicle equipped with the quietest tires available is 3-10 dB lower than when equipped with the tirrs being tested.

8. Reference Material Suggested reference material is as follows.

8.1 ANSI Si 1-1960 (R1971), Acoustical Terminology

8.2 ANSI Si. 2-1962 (R1971), Physical Measurement of Sound

8.3 ANSI SI 4-1971, Specification for Sound Level Meters

8.4 SAL Recommended Practice J 184. Qualifying a Sound Data Acquisition System

8.5 Tire and Rim Association Yearbook

8.6 SAE Publication SP-373, Truck Tire Noise

8.7 G. R Thurman, “Effect of Road Surface and Bed Clearance on Truck Tire Noise " Paper 740607 presented at SAE West Coast Meeting. Anaheim, California, August 1974 The ANSI documents are available from the American National Standards

Institute. Inc., 1430 Broadway, New York, New York 10018

APPENDIX

Al. An A-weighted sound level not exceeding 85 dB determined in ac- cordance with this recommended practice, is consistent with present best current practice for cross ribbed tires in normal states of wear It is general experience that thr sound level of unworn tires is significantly less than (hat of worn tires

ated bv highway truck tires. Rib type tires generally produce lower sound

levels on smooth surfaces than on surfaces having a textured finish such as that brushed in during construction. Differences as great as 5 dB have been

observed between sound levels obtained on very smooth and coarse concrete

surfaces for tires producing relatively low levels of sound. For cross-ribbed

tires, however, generated sound levels have been found to not differ by more

than approximately 1 dB for given tire types on a variety of Portland cement

concrete surfaces judged to be relatively smooth. For these reasons, the vehicle path description in paragraph 3 2 is sufficient to provide for reproducible sound levels for cross-ribbed tires, within the expected accuracy of such measurements (±ldB), and to provide surface-dependent relative sound

levels for rib type tires A3. Persistence of tire sounds after the passage of the vehicle and the tonal components of these sounds are properties of certain types of tires which tend

to occur concurrently. Both are factors that direct attention to the sound, and

are important determinants of the acceptability of thr sound.

29
5, APPENDIX B. AC0UBTTGA1. MEASUREMENT TEST UROGRAM

The operational procedures and measurement/analysis instrumentation

utilized in this load/deflection study were similar to that used in previous

DOT/NRS truck tire noise studies. In the following sections detailed

descriptions are provided of the vehicle configurations, test tires, field

test site utilized for data acquisition and the operational test procedure.

5.1. Field Test Rite

The dynamometer course at the U.S. Army Proving Ground located in Yuma,

Arizona, was selected as the test site for the acoustical data acquisition

phase of the program. Utilization of this site was arranged through

agreement with the U.S. Army Test and Evaluation Command, Aberdeen ^roving

Ground, Aberdeen, Maryland.

The dynamometer course is approximately 2 miles (3219 m) long with 500

foot (152.4 n) radius turn-arounds at each end. The roadway is 30 feet

(9.1 m) wide, near-level (0.8 percent grade) and is surfaced with a high

strength asphalt. A 600-foot (182.9 m) test section was established at the

southwest end of the course. A maintenance shelter and storage building

located adjacent to the dynamometer course were used to store test tires and as the area where the tires were mounted on the test vehicles. Figure B-l

shows an overall view of the test site with the location of the test section

and maintenance facilities noted. A photograph showing the surface details

of the dynamometer course is presented in Figure B-2

To comply x^ith the measurement area requirements of SAE J57a (see

Appendix A) , an asphalt pad was constructed adjacent to the dynamometer

course roadway. This triangular-shaped pad consisted of three rectangular

sections of asphalt erach 3 inches (7.6 cm) thick, 10 feet (3.0 m) wide and

600, 400, and 200 feet (182.9, 121.9, and 61.0 m) long, respectively. The

pad was allowed to cure for two weeks after construction and then was sealed

using a commercial driveway sealer. Figure B-3 is a photograph showing the

test section on the dynamometer course roadway and the measurement area pad.

5.2. Test Tires

A set of four bias-ply rib tires (tire A) and a set of four bias-ply

cross-bar tires (tire E) were tested in the acoustical measurement portion

of this program. These were the same types of tires as listed in Table 1. The

test tires were always mounted on the drive axle of the test vehicle. Rib

tires, which had a characteristic tire noise level that was known to be as low

as or lower than that of the two sets of test tires, were mounted on the

steering axle. The characteristic tread patterns for the test tires are shown in

30
Figure B-l. Plan of dynamometer course at the U. S. Army Yuma Proving Ground,

Yuma, Arizona, showing the location of the test section and maintenance facility.

31
*
Figure B-2. Pavement surface details of the dynamometer course.

32

Figure

B-3.

A

view

of

the

test

section

established

on

the

dynamometer

course

roadway

and

the

measurement

area

pad.

££
Figure B-4. The average tread depth— and average Shore hardness- for these

tires are also indicated.

For these tests the inflation pressures were set to the desired value

and the vehicle run for a minimum of ten miles to allow the tire to warm up.

The vehicle was then stopped and the inflation pressures were again adjusted

to the desired value to maintain constant tire deflection. Immediately

following this, the acoustic measurement test runs were made.

TIRE A TIRE B

o New bias-ply rib

o Average tread depth -- 16/32 inch , 0 Average Shore‘s hardness - 50

° New bias-ply cross-bar

o Average tread depth —

29/32 inch

° Average Shore hardness - 64

Figure B-4. Characteristic tread element pattern, average tread depth, and

average Shore hardness for the test tires.

£/ Tread depth measurements were taken at four ecmally spaced locations

around the tire circumference. The device utilized for this measurement

was simply a depth gage with 1/32 inch graduations. The operator located

the depth gage over a major groove (not over sipes or other small

grooves), depressed the probe into the groove, and noted the tread depth

directly from the instrument.

— The Shore hardness of the tread rubber was determined by ASTM test method

D2240-68 [19]. A type A durometer (for soft materials) was utilized in

the following manner: the durometer was held in a vertical position with

the point of the indentor at the center of the tread face. The presser

foot was applied to the specimen as rapidly as possible without shock,

keeping the foot parallel to the specimen surface. The scale was read

five seconds after the presser foot was in firm contact with the specimen.

The reported values represent the average for readings taken at

approximately the same four locations as the tread depth measurements.

34
‘>.3. Test Vehicle

The test ve^yle utilized in this study was an International Harvester

Model 1700 4 x 2~~ single-chassis truck with a conventional cab. This

vehicle was equipped with 10-hole Budd wheels, 392 CID gasoline engine,

5-speed transmission and 2-speed axle. All tests were run in a coastby mode

at 50 mph (80.5 km/hr). An overall view of the vehicle is shown in Figure

B-5. The loading conditions of the test vehicle and the tire inflation

pressures are listed in Table 7 in Section 3.1.

5.4. Test Procedure

The test procedure utilized was essentially identical to that specified

In SAE J57a; however, the following exceptions should be noted:

"Fast" meter response was utilized.

The hard surface (vehicle path and measurement area) was sealed

asphalt.

The distance between the point of entrance and point of exit of the

test section was 600 feet (182.9 m)

Mud flaps were left on the vehicle during testing.

The components of the data acquisition and recording instrumentation,

plus the automatic tape recorder control and elapsed time system utilized are shown in Figure B-6.

Three tape switches — one immediately before the test section and one each at the beginning and end of the test section — were used to start and

stop the recorder and to mark the data tapes to designate the start and end of

data. The tape switches at the beginning and end of the test section were

also used to control an elapsed time system which provided a direct readout of

average vehicle speed in miles per hour.

The acoustic measurement system consisted of a one-inch condenser

microphone, a battery-operated microphone power supply (to supply the

polarization voltage to the microphone), a step attenuator which provided the

capability for selection of gain over a range of 60 dB in 10 dB steps, and a —10 /The commercial vehicles utilized are identified in this report in

order to adequately describe the vehicles on which the test tires

were mounted throughout this program. In no case does such

identification imply recommendation or endorsement by the National

Bureau of Standards, nor does It imply that these vehicles were

necessarily the best available for the purpose. —

11 / The nomenclature 4x2 relates to the number of wheel positions —

4, and the number of driven positions — 2, but has no relationship

to the number of tires — 6. Therefore, a 6 x 6 would have 10

tires mounted at 6 wheel positions, 6 of which are driven.

35
r

36
Figure

B-6.

Data

acquisition

and

recording

instrumentation

plus

automatic

tape

recorder

control

and

elapsed

time

system.

LI

TEST

SECTION
tape recorder with two direct record analog data channels and one "FM” timing

channel. The system included both a flat frequency response hold capability

-— which provided an indication as to whether or not a tape channel had

saturated (saturated runs were repeated) — and an A-weighting hold capability — which provided a direct reading, in the field, of the maximum A-weighted

sound level observed during a passby without having to return to the

laboratory for analysis of the tapes. The measurements were performed

out-of-doors; therefore, a windscreen was placed over the microphone to reduce

the noise produced by wind passing over the microphone grid. A hand-held

rotating vane anemometer was used to measure wind speed. No measurements were made for wind speeds greater than 12 mph (19.3 km/hr). A single point

calibration utilij^g a pistonphone which produced a 124 dB sound pressure

level (re 20 yPa) — at a frequency of 250 Hz was used for system calibration

in the field. Calibration tones were recorded on the data tape once each hour

as well as at the beginning and end of each data tape. Figure B-7 shows the

microphone location and associated instrumentation in the field at the Yuma

Proving Ground test site.

Once the data had been recorded, the analog tapes were returned to the

National Bureau of Standards for reduction and analysis. Figure B-8

identifies the equipment which was utilized for analysis purposes. Each tape was played back a channel at a time through the real-time analyzer. An

interface-coupler was necessary to make the real-time analyzer compatible with

a mini- computer. When a timing signal appeared on the analog tape, the

computer was instructed to start sampling the digital data from the real-time

analyzer. A real-time analyzer time constant of 0.2 second above 200 Hz and one which below 200 Hz increased linearly to 3.15 seconds at 12.5 Hz was utilized to obtain the root-mean-square (rms) value of the level. Once all

data had been analyzed, the computer stored the data and dumped it onto

digital magnetic tape. This tape was formated to be acceptable to the large

NBS computer which was utilized for further analysis. For the purposes of

this report only the maximum A-*weighted sound level data are discussed.

One-third octave band data were also obtained but are not reported here.

12 / “— A pistonphone generates a reference sound pressure of 124 dB

(re 20 pPa) only at the standard atmospheric pressure of 760 mm Hg. For

ambient pressure conditions other than standard the actual level will vary

from the reference value of 124 dB (e.g., 760 + 10 mm Hg corresponds to

124 +0.1 dB)Because the magnitude of this departure from the reference

level was small for the range of ambient pressure conditions at the Yuma

test site, no corrections were made to the data.

38
line

perpendicular

to

the

vehicle

pat

6C

H- ooc

•-t fDt0I •^1 3 O

H* < n 3

it

n o 3 ay h* o3 <

(D H* O rr o y 3 3

rr

fD 3 y h*o o o

-a

t-h

y

fD

O

fD 3

rr fD

H*

O

Ln

O • 3

N3 rrH* 3 2

i-r> s; if H- O rr 3 y

rr rr 3“ 3*

fD (D O rr

(D (D 3 m

rr rr

<Drf <

t-* fD ,H* y 3 HfD O

l-1 O (D

r—r» • <

(D

H

y

y

H- fD O

i-1 rr

(D rfH*

rr *3

rf

O 3 Q. < j, 3 3

I—* oc 3 3

r—1 rr O 3 3 G.

00
40

Figure

B-8.

Data

reduction

and

analysis

system.
6. REFERENCES

[1] Anon., Truck Noise-T, Peak A-Wel ghted Sound Levels Due to Truck

Tires, T7. S. Department of Transportation p eport No. OST-ONA-71-9

(National Bureau of Standards, Washington, D.C., September 1970).

[2] Tetlow, D., Truck Tire Noise, S)V Sound and Vibration _5 (8),

17-23 (August 1971).

[3] Flanagan, W. , Recent Studies Hive Unified Picture of Tire Noise,

Automotive Engineering, 8_0 (4), 15-19 (April 1972).

[ 4 ] Corcoran, D. A., Effects of Operating Parameters on Truck Tire

Sounds, published in SAP Report SP-373: Truck Tire Noise

(Society of Automotive Engineers, Tnc., Warrendale, Pa., October

1972).

[ 5 ] Leasure, Jr., W. A., Corley, D. M. , Flynn, D. R. , and Forrer, J. S.

Addendum to Truck Noise-I, Peak A-Weighted Sound Levels Due to

Truck Tires, U. S. Department of Transportation Report No.

OST/TST-72-1 (National Bureau of Standards, Washington, D. C.

July 1972).

[6] Kilmer, R. D. , Leasure, Jr., W. A., and Mathews, D. E., Truck

Noise T.-C, Pavement Surface Effects on the Ceneration of Truck

Tire Noise, U. S. Department of Transportation Report No.

DOT-TST-76-49 (National Bureau of Standards, Washington, D. C.,

October 197,5).

[7] Anon., The 1976 Yearbook (Tire and Rim Association, Tnc., Akron,

Ohio, 1976).

[8] Society of Automotive Engineers, Inc. , J57a - Sound Level of

Highway Truck Tires, SAE Recommended Practice (Society of

Automotive Engineers, Inc., Warrendale, p a . , 1976).

[9] Anon., Truck Tire Noise, presentation by the Rubber Manufacturers

Association to the Office of Noise Abatement and Control, U. S.

Environmental Protection Agency, Washington, D. C. (November 12,

1971).

[10] Anon., Appendix of Technical Data to supplement the Rubber

Manufacturers Association presentation concerning Truck Tire

Noise to the Office of Noise Abatement and Control, U. S.

Environmental Protection Agency, Washington, D. C. (November 12, 1971).

41
[11] Sakagami, J., The Exper imenln.1 Study of Truck Tire Noise, presented at

the 14th FISITA Congress, London, England (1072).

[12] Underwood, M, C. P., A Preliminary Investigation into Lorry Tire Noise,

TRRL Report LK601 (Transport and Road Research Laboratory, Department of

the Environment, Crowthorne, Berkshire, England, 1973).

[13] Leasure, Jr., W. A., Mathews, D. E., and Rinkinen, W. J., Truck Noise

1-A, Noise Evaluation Tests of Military Truck Tires, U.S. Department of

Transportation Report No. DOT-TST-74-21 (National Bureau of Standards,

Washington, D.C., February 1974).

[14] American Society for Testing Materials, E4-72, Standard Methods of

Verification of Testing Machines , in Part 10, Book of ASTM Standards

1975 (ASTM, Philadelphia, Pa.).

[15] Anon., Engineering Design Information Book (Tire and Rim Association,

Inc., Akron, Ohio, 1977).

[16] Thurman, G. R. , Firestone Tire and Rubber Company (retired), private

correspondence to W. A. Leasure, Jr., Office of Heavy Duty Vehicle

Research, National Highway Traffic Safety Administration, U. S.

Department of Transportation, May 4, 1978.

[17] Clarke, S. E. (ed) , Mechanics of Pneumatic Tires, NBS Monograph 122

(National Bureau of Standards, Washington, D.C., November 1971).

[18] Leasure, Jr., W. A., and Bender, E. K. , Tire-Road Interaction Noise,

Jc Acoust. Soc. Am. _58 (1), 39-50 (July 1975).

4

[19] American Society for Testing and Materials, D 2240-75, Standard Methods

of Test for Indentation Hardness of Rubber and Plastics by Means of a Durometer , in Part 37, Book of ASTM Standards, 1975 (ASTM, Philadelphia,

Pa.).

42
4

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