IRT NO. DOT-TST-76-4

AUTOMOBILE TIRE NOISE:

RESULTS OF A PILOT STUDY AND REVIEW

OF THE OPEN LITERATURE

W.A. LEASURE, JR.

D. E. MATHEWS

M. A. CADOFF

AUGUST 1975

Availability is unlimifed. Document has been released to the National Technical Information Service, Operation's

Division, Springfield, Va. 22161, for sale to the public.

Prepared for

U.S. DEPARTMENT OF TRANSPORTATION

Office Of The Secretary

Office Of Noise Abatement

Washington, D.C. 20590

TECHNICAL REPORT STANDARD TITLE PAGE

1. Report No. DOT-TST-76-4

2. Government Accession No. 3. Recipient's Catalog No.

4. Title and Subtitle Aucomobile Tire Noise: Results of a Pilot Study and

Review of the Open Literature

5. Report Date August 1975

6. Performing Organization Code

7. Author's) W. A. Leasure, Jr., D. E. Mathews, and M. A. Cadoff

8. Performing Organization Report No.

9. Performing Organizotion Name and Address National Bureau of Standards

Department of Commerce

Washington, D.C. 20234

10. Work Unit No. 2130452

1 1 . Controct or Grant No.

13. Type of Report and Period Covered

12. Sponsoring Agency Name and Address Final

Department of Transportation

Office of the Secretary

Office of Noise Abatement

Washington, D.C. 20590

14, Sponsoring Agency Code

15. Supplementary Notes

16. Abstract Automobiles, the primary mode of transportation in the United States, contribute

significantly to the noise environment due to th.e large number in operation. In this

report, one aspect of automobile noise is discussed; namely, the contribution to

overall vehicle noise resulting from the interaction of the tires with the road

surface. The results of this pilot study, which investigated the influence of

selected parameters on automobile tire noise levels, in conjunction with a review of

the open literature, serve as the basis for comparison of parametric trends between

truck (for which an extensive noise data base exists) and automobile tires. As was

the case with trucks, vehicle speed, road surface characteristics and tread design

are major factors affecting automobile tire noise. The effect of pavement surface is more significant for automobile tires than for trucks since the texture within the

tire-road interaction zone is on che same scale as the tread element spacing typical

of passenger ^ar tires. Load and wear, significant factors for truck tires, do not

affect automobile tires as much due to the fact that the majority of automobile tires

utilize rib tread designs. On the basis of the limited data available in the literature, factors such as inflation pressure, number of plies, tire dimensions, tire cord

material, etc. , do not appear to be significant factors affecting automobile tire

noise

.

17. Key Words Acoustics; Automobile; Noise (sound);

Tire noise; Transportation noise.

18. Distribution Statement Availability is unlimited. Document may be

released to the National Technical Information Service, Operations Division, Springfield, Virginia 22161, for sale to the

public

.

19. Security Classif. (of this report) 20, Security Classif. (of this page) 21. No. of Pages 22. Price

Form DOT F 1700.7 (8-69)

KBSIR T5-T52

AUTOMOBILE TIRE NOISE: RESULTS OF A PILOT STUDY AND REVIEW OF THE

OPEIT LITERATURE

W. A. Leasure, Jr., D. Mathews, M. A. Cadoff

Mechanics Division

Institute for Basic Standards

National Bureau of Standards

Washington, D. C. 2023^

April 1975

Final Report

Prepared for

Office of Noise Abatement

Office of The Secretary

Department of Transportation

Washington, D. C. 20590

U. S. DEPARTMENT OF COMMERCE

Rogers C. B. Morton, SecretaryJohn K. Tahor, Under Secretary

Dr. Betsy Ancker-Johnson, Assistant Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS

Ernest Ambler, Acting Director

Ta"ble of Contents

2.

introduction

Field Test ?:

;i-e

2.2.

2.3.

2.1i. Tes^

3

6

1

1

3.1. Tijfe J-iifI.s.~i.o 3.2. Speed, Zreai

3.3. Iread '.'rear Zf

3.h. Effect of Car

3.5.

3.6. Effect cf Mic

3.7.

3.8.

eaure

y: Zisciission and Ccncl

n ?res store and Load

resign and Road Sxn-i

cas3 Construction .

;ns ... 19

-iiects 19

ice Effects 21

32

38

111 hk

52

.X ^

.

53

TO

73
Abstract

AutomolDiles , the primary mode of transportation in the United States,

contribute significantly to the noise environment due to the large number in

operation. In this report, one aspect of automobile noise is discussed; namely,

the contribution to overall vehicle noise resulting from the interaction of the

tires with the road surface. The results of this pilot study, which investigated the influence of selected parameters on automobile tire noise levels, in

conjunction with a review of the open literature, serve as the basis for com- parison of parametric trends between truck (for which an extensive noise data

base exists) and automobile tires. As was the case with trucks, vehicle speed,

road surface characteristics and tread design are major factors affecting automobile tire noise. The effect of pavement surface is more significant for

automobile tires than for trucks since the texture within the tire-road interaction zone is on the same scale as the tread element spacing typical of

passenger car tires. Load and wear, significant factors for truck tires, do not

affect automobile tires as much due to the fact that the majority of automobile

tires utilize rib tread designs. On the basis of the limited data available in

the literature, factors such as inflation pressure, number of plies, tire

dimensions, tire cord material, etc., do not appear to be significant factors

affecting automobile tire noise.

11
1. Introduction

Automobiles are the primary mode of transportation in the United States

.

Even though they are not usually as noisy as trucks , buses and motorcycles , the

total contribution of automobiles to the noise environment is significant due to

the large number in operation — over 90 million.

The basic noise sources for automobiles and trucks are essentially the same — engine exhaust, cooling fan, engine casing radiation, and tires — but they

do not necessarily have the same relative importance for these two vehicles

under the same driving conditions.

Tire noise for automobiles may become a significant contributor to overall

vehicle noise levels at speeds as lov as 35-^0 mph (56.3-6U.6 km/hr). For both

passenger cars and trucks, the exact speed at which the tire-roadway noise

starts to predominate is highly dependent upon tire characteristics, road

surface, vehicle condition, engine-exhaust characteristics, etc.

Since trucks are generally considered to present a more serious tire noise

problem than passenger cars, the majority of the data available in the open

literature have resulted from measurements of truck tire noise[l-6]— .

Rather than conduct a large scale study of automobile tire noise, it was decided by DOT and KBS, that a pilot program should be carried out to

investigate the influence of selected parameters which affect automobile tire

noise levels. This program was intended to serve as the basis for determining

whether parametric trends for truck and automobile tires were similar (therefore

defining the extent of additional noise testing of automobile tires needed^in

the future) to supplement the rather limited data on automobile tire noise— .

The National Bureau of Standards conducted this pilot noise evaluation

program on passenger car tires in the summer of 1973 for the Office of Noise

Abatement, U. S. Department of Transportation. The test design was based on

that utilized by NBS in previous studies of truck tire noise [l ,3 ,^ ,5 ] • Tread

design, wear, speed and pavement surface were the parameters studied. Briefly,

the testing included the following:

—^Figures in brackets indicate the literature references at the end of this report.

2/ — At the onset of this pilot program some limited data were available in the

public domain on automobile tire noise; however, the majority of the information was relative to passenger car interior noise[T].
Noise measurements were made at 25 and 50. feet (7-6 and 15.2 metres) as measured from the centerline of vehicle travel. These distances correspond

to the typical European and American measurement locations

.

A full-size 1973 automobile loaded to a gross vehicle weight of 5000 pounds

(2268 kg) — 1250 pounds/tire — was operated at nominal speeds of 50, 60

and 70 mph (80.55 96.5 and 112.6 km/hr) over three pavement surfaces —

. jointed concrete, continuous poured reinforced concrete and asphalt.

'Bias-ply and "bias-belted tires with six different tread patterns — three

rib-tread and three snow tread — were tested in the new and nominally

. half-worn states of wear. In addition, a radial-ply and a bias-ply set of

tires with identical tread patterns were tested in the new condition only.

A minimum of two test r\ans were made at each operational condition.

The results of the pilot program are presented and discussed in this

report. Additional data that have been reported since the onset of this pilot

program are also discussed[7-10]

.

2
2. Field Test Program

2.1. Field Test Sites

Two test sites were utilized in this study. One was the research runway at

the Wallops Station, Virginia facility of the National Aeronautics and Space

Administration. The other was an unopened section of Interstate 8l near

Carlisle, Pennsylvania. Agreements were reached with NASA and the State of

Pennsylvania for utilization of the respective sites for the data acquisition

phase of the program.

Research rimway k-22 (bearing OhO° and 220°) provided an adequate stretch

of pavement [8750 feet (2667 m) ] and a flat terrain providing a well-defined

reflecting surface without any unusual reflection or attenuation effects. Two

test sections, each 1000 feet (30U.8 m) in length, were established on the

rionway. One test area was designated as the concrete test section while the

other was the asphalt test section. The nominal runway width was 150 feet (^5*7

m) with a center section [50 feet (l5.2 m) wide located at the center of the

runway] of specially constructed substrates including some grooved sections.

Although no lanes-, such as one thinks of as being present on highways , were

marked on the runway, the concrete on either side of the special pavement area

was laid in sections 12 feet (3-7 m) wide and 20 feet (6.1 m) long. For this

test program, the car ran in one of these 12 foot (3-7 m) lanes. Due to the

deteriorated condition of the pavement surface near the edge of the r\mway, the

car ran one lane in from the edge. On the asphalt siirface, a lane was marked

which corresponded to the location of the concrete lane. Figuire 1 shows an overall view of the research runway with the locations of both test sections

noted.

The concrete test section began 265O feet (807-7 m) from the northeast end

of runway h-22 and extended to 365O feet (1112.5 m) • It consisted of a substrate of reinforced, air-entrained Portland Cement concrete with two types

of finishes. They were "C" finish or smooth concrete and "D" finish or textured

concrete. The only difference between the two surface finishes was the method

of final finishing. To the untrained eye, there appears to be no difference

between the two sections. The "C" finish section of pavement was smoothed with

a belt of canvas composition while the "D" finish section utilized a finishing

belt of burlap. Figure 2 is a detailed layout of the concrete test area while

Figure 3 is a photograph of the smooth concrete siirface. Three grooved pavement

sections existed on this portion of the runway. One grooved section extended 75

feet (22.9 ni) into the test area but did not interfere with the line-of-sight

from the truck to the two microphones. However, the other grooved sections

(grooved smooth concrete and grooved textured concrete) did lie between the car and the 50 foot (15-2 m) microphone location.

The effect of the grooves on reflection of sound was not established during

this study; however, the width and spacing of the grooves [l/h inch (0.6 cm) and

1 inch (2.5 cm) respectively] appear to be such that only high frequencies would

be affected. It is felt that the grooves would have little or no effect at

those frequencies (l60-2000 Hz) where most of the tire noise is concentrated.

3
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GROOVEDSMOOTH - CONCRETE

25 (7.6)

500 (152.4) 250 (76.2)

TEST SECTION

TEXTURED

CONCRETE

GROOVED

TEXTURED

CONCRETE

250 (76.2) 500 (152.4)

Figure 2. Plan of concrete test area on runvay h-22. Distances are in feet

(metres). Solid circles designate the tvo microphone locations.

Figure 3. Smooth concrete surface on runway 4-22. Scale is in inches.

5
The asphalt test section began 5700 feet (iJST.^ m) from the northeast end

of runvay k-22 and extended to 6700 feet (20^2. 2 m) . It consisted of a substrate of "B" surface course bituminous concrete — also referred to as "textured asphalt". Reference to Figure k shows that the test section was a continuous surface of textured asphalt with the exception of a grooved textured

asphalt section 150 feet (H5.7 m) long and 50 feet (15.2 m) wide along the

centerline of the runway. Only a small corner of this grooved section was in

the line-of-sight path from the test vehicle to the microphones. Figure 5 shows

the texture of the asphalt test section.

In addition to the concrete and asphalt surfaces at Wallops Station, a third surface — continuous poured reinforced concrete — was investigated.

This surface (roadway of an unopened section of I-81 near Carlisle,

Pennsylvania) was selected since it is typical of Interstate Highway System

construction. However, the surface had not undergone the polishing effect that

could be expected once the roadway is opened to traffic. The roadway consisted

of two 12 foot (3.7 wide lanes with 6 foot (I.8 m) paved shoulders on either

side of a grass covered median strip (see Figure 6). At this site it was not

possible to provide a well-defined reflecting surface. The microphone at the 25

foot (7.6 m) location was at the edge of the shoulder; however, the 50 foot

(15.2 m) microphone was located in the median strip. The land to either side of

the roadway was contoured away from the road surface for drainage purposes

;

therefore, the microphone height for the 50 foot (15-2 m) measurement position

was adjusted so that the two microphones were at the same height relative to the

road surface (see section A-A of Figure 6). The test vehicle ran in the outside

southbound lane. Figure 7 shows a view of the test site looking in a northeast

direction. The surface finish of the continuous poured reinforced concrete

pavement (see Figure 8) was very rough and possessed a characteristic "grain"

which ran perpendicular to the direction of traffic flow.

2.2. Test Tires

A total of eight tire types were investigated during the conduct of this

study. The sample of test tires included three rib-tread tires, three

snow-tread tires and two rib retreads. A photograph showing the tread designs

of each of the test tires is given in Appendix A. Additional details of carcass construction and materials are shown in Table 1. All test tires were size H

78-15, load range B (with the exception of the two retreads which were size G

78-15 and GR 78-15 )•

6
150 (45.7)

100 (30.5)

50 (15.2)

N

TEXTURED ASPHALT

GROOVED

TEXTURED

ASPHALT

25 (7.6)

50 (15.2)

TEST SECTION

500 (152.4) 250 (76.2) 250 (76.2) 500 (152.4)

Figure h. Plan of asphalt test area on runway h-22. Distances are in feet

(metres). Solid circles designate the two microphone locations.

Figure 5- Textured asphalt surface on runway k-22. Scale is in inches.

7
SECTION A-A

48 in

(122cm)

gure 6. Plan of continuous poured reinforced concrete test area on Interstate-8l plus sectional view through the microphone locations.

Solid circles designate the two microphone locations.

8
9
Table 1. Tread design and carcass construction characteristics of the test tires.

TEST TREAD CARCASS

TIRE TYPE TYPE

B Rib Polyester, Bias-Ply

C Rib Fiberglass, Bias-Belted

D Rib Rayon-Belted, Radial-Ply

E Snow Rayon-Belted, Radial Ply

F Snow Polyester, Bias-Ply

G Studded Snow Polyester, Bias-Ply

BR Rib Polyester, Bias-Ply

RR Rib Rayon-Belted, Radial Ply

A special note should be made about the retread test tires. The

question had been raised as to whether radial-ply tires were noisier than

tires of bias-ply or bias-belted carcass construction. In order to address

this question, an attempt was made to locate bias-ply (or bias-belted) and

radial-ply tires which utilized identical tread patterns. It was felt that

noise tests on such tires would allow one to determine whether differences

in observed noise levels were due to differences in carcass construction or simply due to the fact that the tread patterns typically found on radial-ply tires were more "aggressive" (tend toward a snow- tread type

pattern) than conventional rib-tread patterns typically utilized on tires

of bias-ply and bias-belted carcass construction. The attempt, however,

was not successful. For this reason, a set of radial-ply and bias-ply

tires were purchased, the tread was buffed off and the tires were retreaded

with identical rib-tread patterns. The results of the experiment conducted

utilizing these tires are discussed later in the report.

Both new and nominally half-worn tires were tested (retread tires were

tested in the new condition only). The half-worn tires were worn through

actual in-service usage on NBS vehicles utilized for shuttle service

between downtown Washington, D. C. and the NBS Gaithersburg , Maryland

campus. These vehicles averaged 2600 miles (^4183-^ km) per month. The

tires were closely monitored and no uneven wear patterns were observed.

The tires were statically balanced prior to mounting on the vehicles.

This is standard operating procedure for automobile tires. A new tire was

not considered acceptable as a test specimen until it had undergone a break-in period of sufficient mileage under actual driving conditions to ensure the removal of all mold marks and manufacturing irregularities

.

Imnediately prior to the actual noise testing of a given set of tires, a warm-up procedure was followed which normally required a minimum trip of

approximately 10 miles (l6.1 km).

10
Two characteristic measurements were made for each test tire — tread depth

and shore hardness. The resultant data are tabulated in Appendix A.

Tread depth measurements were taken at four equally spaced locations around

the tire circumference. The device utilized for these measurements was a depth

gage with 1/32 inch (0.8 mm) 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

D-22^0-68[ll] . A type-A durometer (for soft materials) was utilized in the

following manner: the dirrometer 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.

2.3. Test Vehicle

, The test vehicle utilized throughout this program was a 1973 Plymouth Fuuy

II— which was rented from the General Services Administration. The vehicle was equipped with a V-8 engine ( 3l8 CID), automatic transmission and H 78-15 tires.

The car was operated in a loaded condition. The test loads represented 100

percent of gross vehicle weight and 75 percent of rated tire load at 26 psi (179

X 10 Pa) per Tire and Rim Association recommendations. The vehicle was ballasted with 80 pound (36 kg) sand bags such that all tires were loaded

equally. Figures 9a-c show the placement of the sand bags within the car: two

bags in the front — one on the passenger seat and one on the floor (Figure 9a)

;

five sand bags in the rear — four on the floor and one on the seat (Figure 9t)) ; and one or two sand bags in "che trunk (Figure 9c)- When the fuel tank was full

only one sand bag was placed in the trunk. When the fuel level reached 50

percent, a second sand bag was added in order to maintain comparable loading.

The weight distribution was:

— The vehicle utilized is identified in this report in order to adequately describe the vehicle 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 this vehicle was necessarily

the best available for the purpose.

11
(a)

(c)

A view of the test vehicle showing placement of the sand bags used

to provide the necessary tire loading — (a) front seat, ("b) rear

seat and (c) trunk.

12
front axle 2500 pounds (113^1 kg)

rear axle 2500 pounds (113^ kg)

5000 pounds (2268 kg)

iT-ro^jghout the program the test tires were always mounted on the rear axle

and rib xires vrhose characteristic tire noise level was known to he low were

always mounted on the front axle. The tires were inflated to an air pressure of

26 psi (179 X 10^ Pa)

.

2.h. Test Procedure

Prior to a discussion of the test procedure, a few words of description are necessaiy to estahlish the placement of all instrumentation within the test

section. Figure 10 shows the placement of the microphones, radio transmitters,

and the path of the test vehicle.

The two microphones were located at 25 and 50 feet (7-6 and 15-2 m) from

the centerline of the lane in which the vehicle travelled along a line

pejrpendicular to the path of travel of the test vehicle. Radio transmitters,

activated hy the car running over a tape switch, were located along the test

lane parallel to the path of the vehicle. Coaxial cahles connected the

microphones wi-h -che tape recording and monitoring equipment.

For a noriir-al 5C nph (8O.5 km/hr) mm (the vehicle should be travelling 50

Tuph. (80.5 kn/hr; as i~ passed the microphone array) the driver of the test

vehicle accelerated ~he car to slightly more than the desired speed to

compensate for the deceleration characteristics of the vehicle (during coast-bys

with the engine off)

.

As the car passed over the initial tape sw-itch, the tape recorder was remotely comanded to turn on via the signal from the radio transmitters. The

initial tape switch/radio transmitter system was located such that the tape

recorder was up to speed by the time that the test vehicle entered the test

section. (The location of the initial tape switch was selected based on the

Tnaximum test speed of the vehicle during the program.) Following a time delay a signal was recorded on the Fl-I channel of the tape recorder which designated the

start of data. As the car left the test section, a second tape switch was activated, the radio transiaitter sent a signal to the tape recorder identifying

the end of data and then the tape recorder was remotely turned off. The

data-start and data-end signals were transmitted to the receiver at different

frequencies. An elapsed time clock indicated the time it took for the vehicle

to cover the known distance between the tape switches from which the average

speed of the vehicle was calc'olated.

1 ^
1000 (304.8)

VEHICLE PATH £ ar

T-1

A M-1

25 (7.6)

T-2

50 (15.2)

A M-2 i

• TRANSMITTER

A MICROPHONES

Figure 10. Viev of test section showing instrumentation placement

plus vehicle path (not to scale). Distances are in feet

(metres). Microphones were placed 25 and 50 feet (T«6

and 15.2 metres) from the centerline of the lane in which

the vehicle travelled and along a line perpendicular to

the path of travel. Radio transmitters (activated "by

tape switches) remotely controlled the on/off sequence of

the tape recorder.

Ik
Figure 11 identifies the components that constituted the data acquisition

system — a one-inch condenser microphone, a hattery-operated microphone pover

supply (to supply the polarization voltage to the microphone), a step attenuator

which provided the capahility for selection of attenuation over a range of 60 dB

in 10 dB steps , and a three-channel analog tape recorder . The system included

"both a linear hold capahility — vhich provided an indication as to vhether or not a tape channel had saturated (saturated runs were repeated) — and an

A-weighting hold capahility — which provided a direct reading, in the field, of

the maximum A-veighted sound level observed during a passhy without having to

return to the laboratory for the analysis of the tapes . The measurements were

performed out-of-doors; therefore, windscreens were placed over the microphones

to minimize- the noise produced hy wind passing over the microphone. A single

point calibration utilizing a pistonphone which produced a 12k dB sound pressiire

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 12 shows the

microphone array and associated instrumentation in the field at the Wallops

Station test site.

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

National Bureau of Standards for reduction and analysis. Figure 13 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 real-time analyzer was commanded to begin analysis. A time constant of .2 second above 2 kHz and one which below 2 kHz followed a straight line to 3.15 seconds at 12.5 Hz was

utilized to obtain the root-mean-square (rms) value of the level in each one- third octave band at the output of the analyzer. Once all data had been

analyzed in one-third octave bands , the computer stored the data and dumped it

onto digital magnetic tape. This tape was formatted to be acceptable to the

large IIBS computer which was utilized for further analysis. This

instrumentation system provided for efficient data acquisition and data handling

for the thousands of data points generated for each passby.

Appendix B contains a brief description of the instruments utilized for

data acquisition, reduction and analysis.

15
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test section, Wallops Station site). The array consisted of tvo

tripod-mounted microphones located at 25 and 50 feet (7-6 and 15.2 m)

from the centerline of vehicle travel along a line perpendicular to

the vehicle path.

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3. Parametric Study: Discussion and Conclusions

The data acquisition phase of this program was designed to address the

following questions:

What is the effect of parameters such as tread design, speed,

wear and pavement surface on the noise level of automobile tires?

Are parametric trends for automobile and truck tires similar?

What are the noise generation characteristics of these tires?

In order to develop the data base necessaiy to answer these questions,

the test matrix shown in Table 2 was established. The data acquisition

program followed this pre-defined test plan.

For each operational mode, a minimum of two runs was made. The

maxim-um A-weighted sound level data for all test rims are tabulated in

Appendix A. Also included are photographs showing characteristic tread

design patterns of the test tires and the associated tread depth and rubber

hardness. In this section, the data for the 50 foot (15.2 m) microphone

location are the basis for summarj^ plots which are presented to show the

effect of tread design, speed, wear and pavement siirface on the noise

levels generated by this sample of automobile tires. Also presented are selected spectral data which provide additional insight into passenger car tire noise as well as a comparison of 25 and 50 foot (7.6 and 15-2 m)

measurements with respect to recommending a microphone location for future

standards. At present, SAE J5T specifies a 50 foot (15.2 m) distance for

truck tires; however, experimenters have found that for passenger car tires

under certain combinations of road surface, vehicle speed, and tire tread

design, coastby sound levels using a 50 foot (15.2 m) microphone distance

(from vehicle path centerline) approach the ambient levels at many test

sites. Therefore, in order to improve the signal to noise ratio, some studies have utilized a microphone placed 25 feet (T.6 m) from the

centerline of vehicle travel[8].

3.1. Tire Inflation Pressure and Load Effects

For this prograon the inflation pressure and tire loads were held

constant. In the case of truck tires, changes in load were found[l,2,3] to

significantly affect the noise level generated by tires with cross-bar

(snow tread) tread patterns while noise from tires with rib type tread

patterns were relatively unaffected by load changes . However , data

reported by Hillquist and Carpenter [8] showed variations of only about 1 dB

in A-weighted sound level for bias-belted and radial- belted passenger car tires with continuous rib and discrete block tread patterns over a vehicle

weight range of h'JOO to 6370 po\ands (2132-2889 kg). These weights

represented 85-115 percent gross vehicle weight and 75-100 percent of tire

load ratings. Later work by Veres [10 ] also showed changes in sound level

19
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20
to be on the order of 1 dB between minimum (curb "weight of the car plus the

driver) and maximum (maxim-um design load as recommended by the Tire and Rim

Association) loads — U5iiO-6oUo pounds (2059-2680 kg).

Another factor that could have an influence on tire noise is tire

inflation pressure. A change in tire pressure can be intentionally made or

it can occur unintentionally in service as a result of poor maintenance or temperature. Temperature increases, which result in increases in tire

pressure, principally occur through heat buildup in the tire caused by

flexing and friction during extended driving. Hillquist and Carpenter [8]

studied the effect of inflation pressure on A-weighted sound levels by

making measurements while the^tire inflation pressure was varied over the

range 12 to 36 psi (82.7 x 10 - 2l;8.0 x 10 Pa) (+12 psi around a control

pressure of 2h psi) in increments of h psi. This was felt to be

representative of the range of inflation pressiires one is likely to

encounter in "normal" driving conditions. The results showed that the

noise levels tend to increase with increasing pressure and decrease with

decreasing pressure; however, the changes were not found to be significant.

Until a change of +Q psi from the control pressiire was achieved,

differences between the passby noise levels at the control pressure and the

test pressure were less than 1 dB. Further pressure changes resulted in

little or no additional changes in passby noise levels.

3.2. Speed, Tread Design and Road Surface Effects

It is difficult to distinguish clearly among the effects of speed,

tread design and road surface. Data are typically presented as maximum

A-weighted sound level versus speed, with tread design and road surface as parameters

.

Hillq\iist and Carpenter[8] and Veres [10 ] report increases in

A-weighted sound level on the order of 8-l8 dB for passenger car tires as the speed increases from hO-10 mph (6U.U-112.6 km/hr) . This corresponds to

sound level increasing as the third to fourth power of speed. The data

from this study shows similar trends with increases on the order of 5-7 dB

for speed changes from 50-70 mph (80.5-112.6 km/hr); with the range of data

being 3-8 dB (see Figures 1^1-16). Richards[9] compared the A-weighted

sound level versus speed for a coastby with the microphone located 25 feet

(7.6 m) from the centerline of vehicle travel and for the identical tire

with one wheel of the automobile on a smooth, highly damped dynamometer

roll in a semi-anechoic room. As can be seen in Figure 17, the hO log

velocity relationship provides a reasonable fit to both sets of data.

Tread design is not as significant a factor in passenger car noise as it is for trucks since most passenger car tires utilize rib-type tread

patterns — either continuous rib or discrete blocks. Hillquist and

Carpenter[8] report that discrete block tread patterns, typical with

radial-ply carcasses, tend to be slightly noisier than continuous rib tread

21
SPEED, km/hr

90

80 90

80

d

Q.

=t OCM

0)

03

T3

LU>

LU

D

O

COQ

70

I

O

UJ

NEW, CONCRETE

o TIRE B

• TIRE C

A TIRE D

A TIRE E

TIRE F

TIRE G

100 110

"T"

60 1

50 60

SPEED, mph

70

Figure 1^. Maximum A-weighted sound level, as measured at 50 feet (l5.2 m)

,

versus speed for a loaded vehicle coast-"by on a concrete surface.

Various types of new tires were mounted on the rear axle of the

automobile.

22
SPEED, km/hr

Q.

3. OCM

a> m

73

LU>

LU

O

(O

Q

LUH

X

g

m

<

90

80-

70

60

80

1 NEW, ASPHALT

o TIRE B

• TIRE C

A TIRE D

A TIRE E

TIRE F

TIRE G

90 100 110

50 60

SPEED, mph

70

Figure 15. Maximiim A-weighted sound level, as measured at 50 feet (l5-2 m) versus speed for a loaded vehicle coast-ty on an asphalt surface

Various types of new tires were mounted on the rear axle of the

automobile

.

23
80

SPEED, km/hr

90 100 110

Q.

OCM

0)

CDd

UJ

>

UJ

->o

CO

Qm

I-I

g

LU

1 <

80

NEW, CPRC

o TIRE B

• TIRE C

TIRE D

TIRE E

TIRE F

TIRE G

T T

A

A

70 -

50 60

SPEED, mph

70

Figure l6. Maximiim A-weighted sound level, as measured at 50 feet (l5-2 m) , versus speed for a loaded vehicle coast-ty on a continuous poured

reinforced concrete surface. Various types of new tires were

mounted on the rear axle of the automobile.

2h
o DYNAMOMETER

• PASS BY

1

30 40 50 60

SPEED, mph

70 80 90 100

Q

Figure 1?. A comparison of the A-weighted sound level versus speed for a coast-hy with the microphone located 25 feet {1.6 m) from the

centerline of vehicle travel and for the identical tire with one wheel of the automobile on a smooth, highly damped dynamometer

roll in a semi-anechoic room[9].

25
patterns. As could be predicted on the "basis of truck tire noise data, the

highest noise levels are produced by snow tires, which possess cross-bar

type tread patterns. In general, the data from this study show the

following trends: (l) on the concrete and asphalt surfaces, the tread

designs clustered into two groups — tires-E, -F and -G (radial and bias snow and studded snow tires) were the noisiest with Tires-B, -C and --D (radial, bias and bias-belted rib tires) being quieter, and (2) on the

continuous poured reinforced concrete surface, the surface effects appear

to completely dominate the effect of tread design. In this case, all the

tread designs cluster closely together with little more than 2 dB

difference between the tire types over the entire speed range. The plotted

data are for new tires; however, the data indicate that there is little

difference between the new and worn state for the tires tested (see Figures

19-21, Section 3.3).

It is obvious that road surface conditions can have a strong influence

on tire noise levels; however, the road surface does not influence the

noise from various tire types in the same way. Normally continuous-rib

tread tires tend to produce higher noise levels on rougher road surfaces

while cross-bar tread tires tend to produce similar noise levels regardless

of the surface. The results of this study also exhibit these trends.

It does appear, however, that road surface can have a much greater

effect on the noise of passenger car tires than on truck tires. This is

due to the fact that the texture within the tire-road interaction area is on the same scale as the tread element spacing typical of passenger car

tires. The scale of interest, which is thought to be important in at least

some tire noise source mechanisms, is pavement macrotextiire . The

macrotexture scale is that appropriate to the overall dimensions of

individual stones in the pavement aggregate — generally of the order of

one or two centimeters and less. This phenomena is evidenced by the

apparent dominance of road surface as the influencing parameter in the case

of the continuous poured reinforced concrete surface — a lateral drag

finished surface which is common on the older sections of the interstate

highway system.

3.3. Tread Wear Effects

Tread wear occurs both through natural abrasion under normal operating

conditions and through faulty wheel alignment. For truck tires, tread wear

was found to be a variable that can greatly affect the sound level

generated by tires[l,2,3] • In general, the noise was found to increase and

then decrease with increasing tire wear. The actual tread depth at which

the maximum noise is generated for any given tread design is not known;

however, this maximum usually occurs at or near the half-worn state of

tread wear. The physical phenomenon responsible for this behavior is

unclear; but, work by Tetlow[2] indicates that change in tread curvatiire is a significant parameter. Tetlow found that when a new tire is ground down

artificially to simulate the tread depth of a worn tire but the tread

radius kept the same as for a new tire, there is much less increase in

sound level than would be expected under conditions of normal wear. In

26
fact, the sound level is scarcely changed at all from that vhen nev (Figure

18). When "both the vorn tread depth and tread radius have "been simulated

artificially, the data ohtained have varied, with the sound levels measured

for these tires sometimes "being very close to those measured for normally

vorn tires. The difficulty is finding a tire vorn in actual over-the-road

service that can serve as a model for the grinding of the tire to he

artificially vorn.

These trends, hovever, do not appear to hold in the case of passenger

car tires. Data from the present study — Figures 19? 20 and 21 — shov

that automobile tire noise either slightly increased or slightly decreased

as the tires vore, hut the changes vere not significant. With the

exception of the studded snov tire on a concrete surface (an increase of h

63 vas observed in the noise level "betveen the nev and half-vorn states of

tread depth), the noise levels for the sample of tires tested in the

half-vorn state of tread depth vere vithin 2 dB of the levels measured vhen

the tires vere nev. The maximum sound level increases vere observed for

tires running on the concrete surface. It should be noted that these test

tires vere vorn. in actual service. Therefore, it appears that tread vear

is not as significant a parameter for automobile tires as it is for truck

tires

.

This conclusion is further substantiated by the data of Hillqulst and

Carpenter [8] . They utilized both service vorn tires and mechanically vorn

tires vhich vere run in for about 100 miles prior to testing. They report — for continuous- rib, discrete block and blank (full tread depth but no tread pattern) tread designs — that for both naturally and artificially

vorn tires, passby noise levels increased on the order of 2 dB betveen the

nev (full tread depth) and half-vorn state of tread vear. As vear

increased, no further increase in sound level vas noted.

It should be pointed out that this appears to be the first citation in

the literature of any success vith simulation of tire vear through

artificial buffing techniques. No details vere provided as to hov this vas

achieved; that is, hov the appropriate tread depth and tread radius vere

selected. The influence of tread curvature appears to be more important

for cross-bar type tread designs vhich vere not investigated in the

Eillquist and Carpenter study. This could explain the success of the

buffing technique in this case.

The relationship betveen tread depth and tread vear and the effect on generated tire noise should be further investigated so that the data

necessary to allov the prediction of tire noise levels at various stages of

vear based on measurements made utilizing artificially vorn tires can be

provided. This is an extremely important factor if tire noise regulations

are promiilgated. From a certification standpoint , one is primarily

interested in that state of tire vear that results in the maximum noise

level for that particular tire type. Without the aid of a predictive

model, it vould be necessary to develop a curve of noise level versus tread

depth so that the maximum noise level that could be expected for a given

tread design, or a class of tread patterns, could be identified — a costly

and time-consuming process.

27
LU

>

LU

_J

Q

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Q

LJ

h-X

o

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I <

X

<

90 60

SPEED, km/hr

80 100 120

I I

1—r~

"HALF-WORN" BY

T 1

80

GRINDING TO CURVATURE

OF A HALF-WORN TIRE

NATURALLY

HALF-WORN TIRE

"HALF-WORN" BY

GRINDING TO CURVATURE

I OF A NEW TIRE

^NEW TIRE

/

70 i

40 50 60 70

SPEED, mph

80

•Figure l8. The effect of tread curvature on tire noise for a typical cross-bar

tire when (l) new, (2) "half-worn" by grinding to curvature of a half-worn tire, (3) "half-worn" by grinding to curvature of a new

tire, and (U) naturally half-worn tire [2].

28
0

TREAD DEPTH, cm

1.00 2.00

d

it

o

o

m

o

LU>

LU

90 -

o TIRE-B

• TIRE-C

A TIRE-D

TIRE-E

TIRE-F

TIRE-G

CONCRETE

D

O

COG

lU

I

O

LU

80

<

LU

X

<

70

0.25 0.50 0.75 1.00

TREAD DEPTH, in.

i-'axici'an A-veighted soxmd level, as measured at 50 feet (15.2 m) versus vear for a loaded vehicle coast-by on a concrete surface.

Various types of tires vere mounted on the rear axle. Vehicle

speed vas 60 nrph (96.5 km/hr).

29
Q.

oCM£ 90

T3

UJ>

LU

3

O

CO

Q

LU

\-

I

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LU

X

<

80

70

<

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LU

TREAD DESIGN, cm

1.00 2.00

o TIRE-B

• TIRE-C

A TIRE-D

TIRE-E

TIRE-F

TIRE-G

ASPHALT

1

0.25 0.50 0.75

TREAD DEPTH, in.

1.00

Figure 20. Maximum A-veighted sound level, as measured at 50 feet (15.2 m)

versus wear for a loaded vehicle coast-by on an asphalt surface.

Various types of tires vere mounted on the rear axle. Vehicle

speed was 60 mph (96.5 km/hr).

30
d

Q.

OCMO

OQ

a

>

LU

TREAD DEPTH, cm

1.00 2.00

0) 90

OTIRE-B

• TIRE-C

A TIRE-D

A TIRE-E

TIRE-F

TIRE-G

CPRC

D

O

COQ

UJI-I

g

LU<

X

<

80 -

-2

<

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LU 701 '

0.25 0.50 0.75

TREAD DEPTH, in.

1.00

Figure- 21. Maximum. A-weighted sound level, as measured at 50 feet (l5-2 m) versus wear for a loaded vehicle coast-Toy on a continuous poured

reinforced concrete surface. Various types of tires vere mo\mted

on the rear axle. Vehicle speed was 60 mph (96.5 km/hr)

.

31
Although a "break-in period has been utilized by tire researchers prior

to making noise measurements, the length of the break-in period has varied.

Veres [10 ] investigated this problem and his results are shown in Figure 22.

He made tire noise measurements when the tires vere new and at mileage

intervals of 50, 100, 150, 200, 300, UOO, 500, 750 and 1000 miles (80.5,

160.9, 2kl.k, 321.8, U82.T, 6I13.6, 80U.5, 1206.8 and I609 km). The data

show that after approximately 200 miles (321.8 km), the noise level

stabilized and did not vary significantly up to 1000 miles (1609 km) . No

other data of this nature has been found in the literature.

3.^. Effect of Carcass Construction

As discussed in Section 2.2., the question had been raised as to

whether radial-ply tires were noisier than tires of bias-ply or bias-belted

construction. In order to isolate the effect of carcass construction from

the effect of tread design, an attempt was made to locate tires with

identical tread patterns of each of the three carcass types. Such tires

could not be located; therefore, NBS purchased a set of new bias-ply

(078-15) and radial-ply (CRT 8-15 ) tires, had the existing tread buffed off

and had the tires retreaded with identical rib tread patterns (see Appendix

A for a photograph of tread pattern) . These experimental test tires are identified as tire-BR (bias-ply retread) and tire-RR (radial-ply retread)

in the test matrix (see Table 2).

The A-weighted soiind level data for these tires are shown in Table 3.

The data are as measured at the 50 foot (l5-2 m) microphone location for a vehicle speed of 60 mph (96.5 km/hr) . One-third octave band spectral data

for the identical test conditions are shown in Figures 23, 2k and 25

corresponding to tests on the concrete, asphalt and continuous poured

reinforced concrete surfaces, respectively.

On the basis of this limited experiment, the data indicate that, in

general, the bias-ply tires exhibit the higher noise levels. This was the

case in all but three of the eighteen test runs. The differences in

maximum A-weighted soimd level were always less than 3 dB and in one-half

of the cases, 1 dB or less. The fact that many people consider radial-ply

tires to be noisier is probably attributable to the following two reasons. First, the tread patterns typically found on radial-ply tires are more

"aggressive" — more like a snow tire than a summer tire — than

conventional rib tread patterns typically utilized on tires of bias- ply or bias-belted construction. Second, the rubber grommets in an automobile

suspension tend to attenuate vibrations above 100 Hz. As reported by

Potts [12] for H78-I5 tires, all the resonances of bias-ply and bias-belted

tires lie above this cutoff frequency, therefore, minimal transmission into

the automobile of road disturbances occurs. However, in the case of a radial tire, the first three modes are below 100 Hz. The radial tire

demonstrates a proliferation of radial resonant frequencies and strong low

level resonances which promote direct passage of sharp disturbances into

the automobile chassis.

32
TREAD WEAR, kilometers of travel

Figure 22. Results of an investigation of the effect of tread wear

on the A-weighted sound level during the initial 1000

miles (1690 km) of travel. Vehicle speed was hO mph

{6h.k km/hr) . Surface was concrete[lO ]

.

33
Table 3. Maximiini A-weighted sound level (in dB re 20 yPa) as measured

at 50 feet (15-2 m) for test runs at 60 mph (96.5 km/hr) on a concrete, asphalt and continuous poured reinforced concrete (CPRC)

surface. The test tires had "bias-ply and radial-ply carcass constructions with identical rib tread patterns.

TIRE TYPE

MPH (km/hr)

PAVEMENT SURFACE

CONCRETE ASPHALT CPRC

Bias -Ply

Radial-Ply

50 (80.5)

60 (96.5)

TO (112.6)

50 (80.5)

60 (96.5)

TO (112.6)

65.8 6t.O

Tl.O TO.^

T1.6 T2.1+

6T.6 6T.2

69.8 TO.O

T2.0 T1.8

68. U 68.2

T2.8 TO.O

T3.2 T3.1+

66.1+ 66.

k

TO. 6 69.2

T2.6 T2.1+

T3.1+ T3.1+

T6.6 TT.O

T9.8 T8.8

T2.6 T2.2

T6.2 T5.8

TT.2 T6.2

3h
• TIRE — BR

o TIRE — RR

CONCRETE

o

Q.

oCM

QQ

LU>

80 -

^ 70

<

m

LU>

<

O

O

Q

CCI

h111

60

50 J L J I I I I I I I L I ' I I I I I L 0.1 1.0

BAND CENTER FREQUENCY, kHz

10.0

Figure 23. One-third octave band frequency spectra for tires BR and

RR as measured at 50 feet (15-2 m) . The vehicle was loaded and operated in a coast-by mode at a speed of 60

mph (96.5 km/hr) while running on a concrete surface.

[A-veighted sound levels: tire-BR, 71-0 dB ; tire-RR,

69.8 dB.

]

35
C5 Q.

OCM

OQ

>

UJ

_J

Q

z

<

QQ

in

>

<

o

o

Q

HIz

o

• TIRE — BR

o TIRE — RR

ASPHALT

80

60

50 I ' I L '

I I

« ' ' I I 0.1 1.0

BAND CENTER FREQUENCY, kHz

10.0

Figure 2h . One-third octave band frequency spectra for tires BR and

RR as measured at 50 feet (15-2 m) . The vehicle was loaded and operated in a coast-by mode at a speed of 60

mph (96.5 km/hr) while running on an asphalt sirrface.

[A-weighted sound levels: tire BR, 72.8 dB; tire-RR,

70.6 dB. ] . . .

'

36

'1

I I
• TIRE-BR

o TIRE-RR CPRC

80

70 -

h 60 -

50 J \ I L J I I I I I L J I I i I I I L 0.1 1.0

BAND CENTER FREQUENCY, kHz

10.0

Figure 25. One-tMrd octave "band frequency spectra for tires BR and

RR as measiired at 50 feet (l5-2 m) . The vehicle was loaded and operated in a coast-hy mode at a speed of 60

mph (96.5 km/hr) vhile running on a continuous poured

reinforced concrete (CPRC) surface. [A-veighted sound

levels: tire-BR, T616 dB; tire-RR, 76.2 dB.]

37
3.5- Miscellaneous Effects

The parameters discussed in this subsection were not investigated in

the present study; however, for completeness, the findings of other

researchers are discussed.

a. Number of Plies

Yurkovski, et al[l3] report that using two plies rather than four

slightly increases the noise level. They speculated that this is due to

lower hysteresis losses in the tires as a result of the lower rubber

content, and consequently the high-frequency vibrations caused by obstacles

in the road are damped by the tires to a lesser extent.

b. Tire Reinforcing Fabric

¥iener[lU] tested tires of various construction and observed a remarkable constancy of the tire noise spectrum and level with respect to

changes in the fiber material of the tire reinforcing fabric, e.g., nylon,

rayon, etc., for a given set of operating conditions. Figure 26 shows two

spectra obtained on a rough road at 50 mph (80.5 km/hr) for tires

containing two different synthetic fibers in their reinforcing fabric. The

differences in the noise levels shown may be significant, especially those

in the frequency region around 500 Hz. Figure 27 shows similar results

obtained on a smooth road.

c. Tire Dimensions

Hillquist and Carpenter [8] investigated two aspects of tire

dimensions; namely, overall size and aspect ratio (tire sectional

height/sectional width)

.

No significant differences in A-weighted sound levels were observed

for tests utilizing ik and 15 inch tires with the same tread pattern.

However, coastby noise levels increased approximately 2 dB when low aspect

ratio (e.g., "wide oval") tires were compared with more conventional tires.

d. Wet Road Surface

When it rains, a layer of water is present in the contact area between

the tire and the road which affects noise generation. Engler[l5] reports

that higher A-weighted sound levels and different frequency spectra occur

on a wet road and are chiefly due to the additional splash noise. Other

European work[l6,lT] show typical increases in the A-weighted sound level

for passenger cars equipped with "summer tires" on the order of 6-10 dB

between data for wet roads as compared to dry road surfaces . Spectral data

on truck tires [3] show considerable increases in sound pressure level at

frequencies above 1000 Hz but little or no increase (0-3 dE) in the

A-weighted sound level. No comparable spectral data have been cited in the

literatiore for passenger car tires. It should be noted that evaluation of

the quantitative descriptions of the surfaces used for the European studies

indicate they are, in general, not typical of those found in the United

States.

38
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FIBER B

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0.1 LO

FREQUENCY, kHz

10.0

Figure 26. Tire noise spectra at constant speed (50 mph, 80.5 km/hr) on a rough road for two different tire types. The microphone was mounted on the outside of the rear fender of a fully-loaded, full

size passenger car[l3].

39
2 MO

o

£ 100

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liJ

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1 1 IIM| 1 1 1 1 1 Ml| 1 1 1 1 1 1 ll|

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1 1 Mill 1 1 1 1 1 1 III 1 1 1 II 1 III

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FREQUENCY, kHz

Figirre 27. Tire noise spectra at constant speed (50 mph, 80.5 km/hr)

on a smooth road for tvo different tire types. The microphone

vas mounted on the outside of the rear fender of a fullyloaded, full size passenger car[l3].

ho
3.6. Effect of Microphone Location

As noted earlier in Section 3, some researchers have found that under

certain comhinations of tread design, vehicle speed, and road surface, the

sound levels for passenger car tires at 50 feet (15.2 m) were approaching

the ambient at many test sites. In order to improve the signal to noise

ratio and to take advantage of the fact that the closer to the source the

microphone is located, the less influence environmental effects (such as thermal gradients rising from the road surface) can have on the propagation

of the sound from source to receiver, some studies have utilized a microphone placed 25 feet (7.6 m) from the centerline of vehicle travel.

Veres [10 ] investigated the effect of microphone location "by making

simultaneous measurements at 25 and 50 feet (7.6 and 15-2 m) . He observed

that the decreases in A-velghted sound level from 25 to 50 feet (7.6 to 15.2

m) averaged 5.8 dB; hovever , the magnitude of the decrease varied with the

tire type and surface texture on which the tires ran. He noted that other

researchers have reported a 5-5 dB average decrease in A-weighted sound

level "between these distances and on the "basis of his data, Veres feels that

this is pro"ba"bly a good estimate. However, due to the significant standard

deviations and the dependency of the decrease on tire type and surface

texture, he recommends that if the actual sound level at 50 feet (15.2 m) is

desired, it should he measured.

Simultaneous measurements were also made during the present study at

microphone distances of 25 and 50 feet (7.6 and 15.2 m) from the centerline

of vehicle travel. The decreases in A-weighted sound level from 25 to 50

feet (7.6 to 15.2 m) o"bserved during this study are tabulated in Table h

(new tires) and Table 5 (half- worn tires). It should be noted that the

concrete and asphalt test sites were "hard sites"; that is, a well-defined

reflecting surface existed between the automobile and measuring microphones.

The continuous poured reinforced concrete test site was a "soft site" — a combination of hard surface (on which the vehicle operated) and grass

between source and receiver. This is the reason that the average

differences for the continuous poured reinforced concrete surface are higher

than those observed for the concrete and asphalt surfaces. The average

decrease (for the hard sirrface sites only) was approximately h.9 dB with a range from U.5-5.2 dB, lower than the average observed by Veres. In

general, the rank ordering of the tires according to noise level would be

the same at either 25 or 50 feet (7.6 or 15-2 m) even though the prediction

from 25 to 50 feet (7.6 to 15.2 m) or vice versa cannot be accurately

predicted for any given set of tires for a particular set of operating

conditions

.

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3.T Spectral Data

In order to gain an understanding of the mechanisms "by vhich tire-road

interaction noise is generated— , one cannot simply look at only single

numher descriptors such as the A-weighted sound level, "but must analyze the

noise in finer detail through spectral analysis. The data for all test runs

in this study have been analyzed in one-third octave hands. Figures 28-33

show characteristic frequency spectra for each of the six automobile tires

tested. Each figure contains three plots corresponding to coast-hy tests

with new tires at 60 mph (96.5 km/hr) on a concrete, asphalt and continuous

poured reinforced concrete surface.

The tire noise spectrum is composed of two parts: a periodic variation

due to the tread pattern and tire nonuniformities and an aperiodic variation

due to road surface cavities. The periodic component exhibits spectral

peaks at discrete frequencies and the aperiodic component exhibits a more

continuous spectrum. The frequencies of the spectral peaks associated with

the tire design can be predicted by calculating the number of tread elements

which pass through the footprint per second. If the distance between

consecutive tread elements is uniform, the sound produced is nearly a pure

tone. Most automobile tire manufacturers, however, do not utilize a uniform

element spacing. The pitch lengths are usually varied in some manner so as to produce a less intrusive sound than a pure tone.

In the case of truck tires [5 ,6] it appeared that the observed spectral

peaks were attributable to tread design alone. However, the author did

caution the reader not to be misled into thinking that the tire noise

mechanism question is simply one associated with tread design alone,

especially since the apparent attainable "limit" with present structural

design — a blank tire (full tread depth but no tread pattern) on a smooth

surface — is only a few decibels lower than current original equipment rib

tires of quiet design. For the automobile tires tested in this study the

major tread element spacings ranged from 0.66 - 1.32 in. (1.68 - 3.35 cm)

which result in predicted fundamental frequencies in the range 800 - l600

Hz. A review of the data shows that these frequencies are apparent;

however, many times the spectra are dominated by peaks at much lower

frequencies

.

Potts [ 12] studied tire vibrations by applying an oscillatory load to

bias-ply, bias-belted and radial-ply tires in the radial, lateral and

circumferential directions. Resonant frequencies were noted for each type

of tire and the corresponding mode shapes observed. The radial direction

— At present, three generic types of tire noise source mechanisms, have been

postulated — aerodynamic, air pumping and vibration. Reference 6 provides a discussion of the existing knowledge pertinent to tire noise source mechanisms

and additional literature references.
c

0.

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0)

ffi T3

80

UJ

LiJ 70

<

ffi UJ

>

<

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Q

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II UJ

60

50

o CONCRETE

• ASPHALT

^ CPRC

TIRE-B

J I L 0.1 1.0

BAND CENTER FREQUENCY, kHz

10.0

FigTore 28. One-third octave "band frequency spectra for tire-B as measured at

50 feet (15-2 m) corresponding to operation of the car in a coast-by mode over concrete, asphalt, and continuous poured

reinforced concrete. The vehicle was loaded and operated at a speed of 6o mph (96-5 km/hr). The test tires were new (full

tread depth)

.

h5
o CONCRETE

• ASPHALT

A CPRC

80 TIRE-C

LUS 70

60

50 J I I I L 0.1 1.0

BAND CENTER FREQUENCY, kHz

10.0

Figure 29. One-third octave band frequency spectra for tire-C as measured at

50 feet (15.2 m) corresponding to operation of the car in a coast-by mode over concrete, asphalt, and continuous poured

reinforced concrete. The vehicle was loaded and operated at a speed of 60 mph (96.5 km/hr). The test tires were new (full

tread depth)

.

he
d

Q.

o

CM

ffi

UJ

>

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<

CQ

UJ

>

<

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o CONCRETE

• ASPHALT

^ CPRC

TIRE-D

80

70

60

50' ' ' J I I I I I I

I

'

I I

'

I

I I L 0.1 1.0

BAND CENTER FREQUENCY, kHz

10.0

Figure 30. One-third octave "band frequency spectra for tire-D as measured at

50 feet (15 • 2 m) corresponding to operation of the car in a coast-hy mode over concrete, asphalt, and continuous poured

reinforced concrete. The vehicle was loaded and operated at a speed of 60 mph (96.5 km/hr). The test tires vere new (full

tread depth)

.

hi
o CONCRETE

• ASPHALT TIRE-E

^^ CPRC

Q. 80 -

BAND CENTER FREQUENCY, kHz

Figure 31. One-third octave "band frequency spectra for tire-E as measured at

50 feet (15.2 m) corresponding to operation of the car in a*

coast-by mode over concrete, asphalt, and continuous poured

reinforced concrete. The vehicle was loaded and operated at a speed of 60 mph (96.5 km/hr). The test tires were new (full

tread depth)

.

h8
o CONCRETE TIrE F

• ASPHALT

0.1 1.0 10.0

BAND CENTER FREQUENCY, kHz

Figure 32. One-third octave band frequency spectra for tire-F as measured at

50 feet (15.2 m) corresponding to operation of the car in a coast-by mode over concrete, asphalt, and continuous poured

reinforced concrete. The vehicle "was loaded and operated at a speed of 60 mph (96.5 km/hr). The test tires were new (full

tread depth)

.

^9
Figiare 33. One-third octave band frequency spectra for tire-G as measured at

50 feet (15 -2 m) corresponding to operation of the car in a coast-by mode over concrete, asphalt, and continuous poured

reinforced concrete. The vehicle "was loaded and operated at a speed of 60 mph (96.5 km/hr). The test tires vere new (full

tread depth)

.

50
resonant frequencies for HT8-15 tires are shown in Table 6. The radial

resonant frequencies resiolt from road induced vibrations caused by road

discontinuities such as pavement expansion joints and road asperities and

tire induced vibrations caused by circumferential variations in tire

uni formity

.

It appears probable that the lower frequency peaks observed in the sound

spectra are associated with vibration induced noise source mechanisms . It is

difficult to correlate passby spectral peaks with the resonant frequencies shown

in Table 6 on a one-to-one basis since the sound spectra at a stationary

observation point along a roadway are complicated by the motion of the source of

sound — the spectra change with time as the relative positions of the tire and

the observer change. The Doppler effect contributes an additional shift in

frequencies which also changes as the relative position of the tire and observer

change

.

Table 6. Radial direction resonant frequencies, in hertz, of

HT8-15 automobile tires [12].

MODE NUMBER BIAS-PLY BIAS-BELTED RADIAL-PLY

1 li+0 l6h 59

2 168 215 80

3 96

k 112

5 130

6 151

7 278 175

8 312 188

9 k20

10 570

51
3.8. Conclusions

Based on the data obtained during the conduct of this test program and a reviev of the open literature, the following conclusions can be drawn:

Vehicle speed, road surface characteristics, tread design and carcass con- struction appear to be the major factors affecting automobile 'tire noise.

The effect of pavement surface appears to be more significant for

automobile tires than for truck tires due to the fact that the textiire

within the tire-road interaction area is on the same scale as the tread

element spacing typical of passenger car tires.

The spectral peaks observed for automobile tires are not predictable from

considerations of tread element spacing and tire rotational rate alone.

Carcass resonant vibration also appears to be a significant influencing

parameter

.

Load and wear, significant factors for truck tires, do not affect

automobile tires as much due to the fact that the majority of the

automobile tires utilize rib tread designs. However, automobile snow tires — as is the case with truck cross-bar tires — are noisier than rib tires

when new and exhibit more of an increase in noise level with wear than rib

tires

.

When tires of both radial-ply and bias-ply construction were equipped with

identical rib-tread patterns, limited tests showed the radial-ply tire to

be the quieter of the two. However, radial-ply tires are typically

manufactured with more "aggressive" tread patterns than conventional rib

tread patterns typically utilized on tires of bias-ply and bias-belted

construction. Also the radial resonant frequencies for the bias -ply and

bias-belted tires are above the lower cutoff frequency of the rubber

grommets in an automobile suspension system while the first three modes for a radial-ply tire are below this frequency. The aggressive tread and lower

reasonant frequencies contribute to the conception that radial tires are noisier than bias-ply or bias-belted tires.

On the basis of the limited data available in the literatirre, factors such

as inflation pressure, number of plies, tire dimensions, tire cord

material, etc. , do not appear to be significant parameters affecting tire

noise

.

A comparison of automobile tire noise levels measured at 25 and 50 feet

{1.6 and 15.2 m) from the centerline of vehicle travel indicate that the

rank ordering of the tires according to noise level would be the same at

either measurement distance even though the relative levels between 25 and

50 feet (7.6 to 15.2 m) or vice versa cannot be accurately predicted for

any given set of tires for a particular set of operating conditions.

52
h. Appendix A

Parametric Study Results

The tabulated values of A-veighted sound level (maximum rms value of

the A-veighted sound level during a passty) as measured at the tvo

microphone locations are reported. The data are assembled according to

tread design and stated vear of the test tires , the speed of the test

vehicle, and the surface over vhich the tests vere conducted. A photograph

shoving the characteristic tread element pattern is presented for each of

the tire types tested. Also included are the average tread depth and Shore

hardness values characteristic of these tires.

53
Figure A-1. Characteristic tread element pattern of tire-B (bias-ply" rit).

The nominal new tread depth for this tire "was 12/32 inch. Shore

hardness values ranging from 58-61 vere observed vith the average

being 60. The nominal worn tread depth for this tire was T/32

inch and the Shore hardness values ranged from 6O-6U with the

average being 62.
Tire B (Bias-Ply Rib)

New Tires - Jointed Concrete

A-veighted Sound Levels , dB

Microphone

Location, ft (m)

Nominal Speed, mph (km/hr)

50 (8G.5) 50 (80.5) 60 (96.5) 60 (96.5) 70 (112.6) 70 (112.6)

25 (T.6)

50 (15.2)

72. U 11. k Ik. 2 Ik.h 78.0 l&.k

67.0 67.^ 70.2 70.6 72.8 7^.2

Worn Tires - Jointed Concrete

A-weighted Soimd Levels , dB

Microphone

Location, ft (m)

Ilominal Speed, mph (km/hr)

50 (80.5) 50 (80.5) 60 (96.5) 60 (96.5) 70 (112.6) 70 (112.6)

25 (7.6)

50 (15.2

72.4 73.0 75.5 75.6 ^7.- 77.-

67.0 61. k 69.8 70.8 -2.6 72.3

New Tires - Asphalt

A-weighted Sound Levels , dB

Microphone

Location, ft (m)

Loniinal Speed, mph (km/hr)

50 (80.5) 50 (80.5) 60 (96.5') 60 (96.5) 70 (112.6) 70 (112.6)

25 (7.6)

50 (15.2)

73.8 ik.O l^.k 76.8 79.0 79.8

69.2 69.2 -^1.'- 70.8 7^.2 75.0

Worn Tires - Asphalt

A-weighted Sound Levels , dB

Microphone

Location, ft (n)

Nominal Speed, mph (km/hr)

50 (80.5) 50 (80.5) 60 (96.5) 60 (96.5) 70 (112.6) 70 (112.6)

25 (7.6)

50 (15.2)

75.2 Ik. 6 11.8 11.0 79.2 80.0

70.6 70.0 72.6 72.2 7^.0 7^.8

Nev Tires - Continuous Poured Reinforced Concrete

A-veighted So^jind Levels , dB

Microphone

Location, ft (in) IToni-al Speed, mph (km/hr)

50 (80.5) 50 (80.5) tz '96.5) 60 (96.5) 70 (112.6) 70 (112.6)

25 (7.6;

50 (15.2)

zL.i c-.: 83.2 65.2 86.8

^5.5 lh.2 11.6 11.2 78.6 79.0

Worn Tires - Continuous Poured Reinforced Concrete

A-weighted Sound Levels , dB

Microphone

Location, ft (m)

Nominal Speed, mph (km/hr)

50 (80.5) 50 (80.5) 60 (96.5') 60 (96.5) 70 (112.6) 70 (112.6)

25 (7.6)

50 (15.2)

19. k 80.2 83.2 83. k 8k. 8 85.6

73.6 73.8 ^c.- ^6.'^ 80.0 80.

U

55
Figure A-2. Characteristic tread element pattern of tire-C (bias-belted rib).

The nominal new tread depth for this tire was 13/32 inch. Shore

hardness values ranging from 59-62 were observed with the average

being 60. The nominal worn tread depth for this tire was 8/32

inch and the Shore hardness values ranged from 6l-62 with the

average being 6l.

56
Tire C (Bias-Belted MTd)

New Tires - Jointed Concrete

A-veighted Sound Levels , dB

Microphone

Location, ft (n)

Noniinal Speed, mph (km/hr)

50 (80.5) 50 (80.5) 60 (96.5) 60 (96.5) 70 (112.6) 70 (112.6)

25 (7.6)

50 (15.2)

71.2 72.0 lh.2 75.1+ 76.1+ 78.6

67.0 67. U 69.6 70.2 72.6 72.6

Wo^n """'"^es - JO'^'ted Concrete

A-veighted Second Levels , dB

Microphone

Location, ft (m)

Nominal Speed, mph (km/hr)

50 (80.5) 50 (80.5) 60 (96.5) 60 (96.5) 70 (112.6) 70 (112.6)

I 25 (7.6)

1 50 (15.2)

72. 12. h 75.0 76.6 78.2 77.8

67.6 68.2 70.2 71.2 72.8 72.6

New Tires - Asphalt ' A-veighted Sound Levels , dB

L^crophone

Location, ft (m)

Nominal Speed, mph (km/hr)

50 (80.5) 50 (60.5) 60 (96.5) 60 (96.5) 70 (112.6) 70 (112.6)

25 (7.6)

50 (15.2)

72.8 72. ii Ik. 6 76.0 77.6 78.0

67.2 68. U 70.8 70.0 72.8 73.6

Worn Tires - Asphalt

A-weighted Sound Levels , dB

Microphone

Location, ft (n)

Nominal Speed, mph (km/h-r)

50 (80.5) 50 (80.5) 60 (96.5) 60 (96.5) 70 (112.6) 70 (112.6)

25 (7.6)

50 (15.2)

7U.6 73.8 ik.Q 75.0 79.6 78.8

69.0 68. k 11. h 11.6 13. h 73.6

I<ev Tires - Cor-tir_-aous Poured Reinforced Concrete

A-veighted So-or-d Levels, dB

'•Hcrcphone

Location, ft (m)

Nominal Speed, mph (km/hr)

50 (80.5) 50 (80.5) 60 (96.5) 60 (.96.5) 70 (112.6) 70 (112.6)

25 (7.6)

50 (15.2)

80.0 80.8 82.2 83.8 86.6 86.1+

7l+.li 73.8 75.8 76. U 79.6 80.2

Worn Tires - Continuous Poured Reinforced Concrete

A-weighted Sound Levels , dB

1-^crophone

Location, ft (m)

Nominal Speed, mph (km/hr)

50 (80.5) 50 (80.5) 60 (96.5) 60 (96.5) 70 (112.6) 70 (112.6)

25 (7.6)

50 (15.2)

81. 1+ 80.6 83.2 8I1.O 85.6 85.6

7I-.2 72.8 77.2 76.2 78.0 79.2

57
Figure A-3. Characteristic tread element pattern of tire-D (radial rib).

The nominal nev tread depth for this tire was 11/32 inch. Shore

hardness values ranging from 6O-65 vere observed vith the average

being 63. The nominal worn tread depth for this tire was 8/32

inch and the Shore hardness values ranged from 6O-6U with the

average being 62.

58
Tire D (Radial Rit)

New Tires - Jointed Concrete

A-veighted Sound Levels , dB

Microphone

Location, ft (m)

Nominal Speed, mph (km/hr)

50 (80.5) 50 (80.5) 6o (96.5) 60 (96.5) 70 (112.6) 70 (112.6)

25 (7.6)

50 (15.2)

73.6 73.0 75.0 75.6 76.0 77.2

69. h 68. ii 70.0 69.6 11. h 72.2

Worn Tires - Jointed Concrete

A-weighted Sound Levels , dE

Microphone

Location, ft (n)

I.oninal Speed, mph (km/hr)

50 (00.5) 50 (80.5) 60 (96.5! 60 (96.5) 70 (112.6) 70 (112.6)

25 (7.6)

50 (15.2)

73.2 73.8 76.2 75.^ 77.0 76.8

67.6 68. U 71.2 70. 6 72. C 73.

C

New Tires - Asphalt

A-weighted Sound Levels , dE

Microphone

Location, ft (m)

Nominal Speed, m"Dh (km/hr)

50 (80.5) 50 (80.5) 60 (96.5') 60 (96.5) 70 (112.6) 70 (112.6)

25 (7.6)

50 (15.2)

72.6 13. h 76.0 75-2 78.2 78.6

6^.8 67.^ 71.^ 70.8 72.5 -^3.8

Worn Tires - Asphalt

A-weighted Sound Levels , d3

Microphone

Location, ft (m)

l.cninal Speed, mph (km/hr)

50 (80.5) 50 (80.5) 6: '96.5) 60 (96.5) 70 (112.6) 70 (112.6)

25 (7.6)

50 (15.2)

lh.6 12.6 16.6 15.6 78.0 78. ii 69.6 67.6 71.2 71.2 13.h 73.8

New Tires - Continuous Pcored Reinforced Concrete

A-weighted Sound Levels, dB

Microphone

Location, ft (n)

Ilominal Speed, mph (km/hr)

50 (80.5) 50 (80.5) 60 (96. 5I 60 (96.5) 70 (112.6) 70 (112.6)

25 (7.6)

50 (15.2)

79.6 81.6 8ii.2 Q3.h 86.2 86.2

Ik. 2 Ik. 2 i6.k 11.6 79.6 79.0

Worn Tires - Continuous Poured Reinforced Concrete

A-weighted Sound Levels , dB

Microphone

Location, ft (m)

ITominal Speed, mph (km/hr)

50 (80. 5) 50 (80.5) 60 (96.5") 60 (96.5) 70 (112.6) 70 (112.6)

25 (7.6)

50 (15.2)

81. li 80.8 81.6 83.0 Q^.k 8I1.6

Ik. 6 75.2 l6.k 76.8 79.8 80.0

59
Figure A-^. Characteristic tread element pattern of tire-E (radial snow).

The nominal new tread depth for this tire was lU/32 inch. Shore

hardness values ranging from 56-60 were observed with the average

being 59- The nominal worn tread depth for this tire was 8/32

inch and the Shore hardness values ranged from 58-68 with the

average being 60.

60
Tire E (Radial Snov)

New Tires - Jointed Concrete

A-veighted Sound Levels , dB

Microphone

Location, ft (m)

Nominal Speed, mph (km/hr)

50 (80.5) 50 (80.5) 60 (96.5) 60 (96.5) 70 (112.6) 70 (112.6)

25 (7.6)

50 (15.2)

78.2 78.8 80.2 79.8 81. U Ql.k

Jh.k 73.0 77.^ 76.0 76.8 76.8

Worn Tires - Jointed Concrete

A-weighted Sound Levels , dB

'

Microphone

Location, ft (m)

ITominal Speed, nph (km/hr)

50 (80.5) 50 (80.5) 60 (96.5") 60 (96.5) 70 (112.6) 70 (112.6)

25 (7.6)

50 (15.2)

79.2 78.8 83.6 82.2 85.8 85.8

Ih.o 75.0 78.2 77.0 80.0 80.

U

Hew Tires - Asphalt

A-weighted Sound Levels , dB

1'Microphone

jLocation, ft (m)

Nominal Speed, mph (km/hr)

50 (80.5) 50 (80.5) 60 (96.5) 60 (96.5) 70 (112.6) 70 (112.6)

I 25 (7.6)

i 50 (15.2)

76.8 77.0 79.2 80.0 83.8 81.8

72.2 71.^ 7^.0 Ih.e 76. U 77.0

Worn Tires - Asphalt

A-weighted Sound Levels , dB

Microphone

Location, ft (m)

Nominal Speed, mph (km/hr)

50 (80.5) 50 (80.5) 60 (96.5) 60 (96.5) 70 (112.6) 70 (112.6)

25 (7.6)

50 (15.2

15.h 16.6 77.0 78.6 81.2 81.2

11. h 71.2 71.8 Ik.h 1^.6 16.

k

New Tires - Continuous Poured Reinforced Concrete

A-weighted Sound Levels , dB

Microphone

Location, ft (m)

rjominal Speed, mph (km/hr)

50 (80.5) 50 (80.5) 60 (96.5) 60 (96.5) 70 (112.6) 70 (112.6)

25 (7.6)

50 (15.2)

79.6 79.0 82.^ 83.0 86.2 85.8

73.8 73.6 77.2 l^.k 19. k 79.2

Worn Tires - Continuous Poured Reinforced Concrete

A-weighted Sound Levels , dB

Microphone

Location, ft (m)

Nominal Speed, mph (km/hr)

50 (80.5) 50 (80.5) 60 (96.5) 60 (96.5) 70 (112.6) 70 (112.6)

25 (7.6)

50 (15.2)

80.8 81.2 Qh.k Qh.o 86.6 86.2

lh.6 lh.8 78.6 18. h Qo.h 80.8

61
Figure A-5- Characteristic tread element pattern of tire-F (bias-ply snow).

The nominal new tread depth for this tire was 13/32 inch. Shore

hardness values ranging from 59-6l were observed with the average

being 6o. The nominal worn tread depth for this tire was 6/32

inch and the Shore hardness values ranged from 59-60 with the

average being 60.

62
Tire F (Bias-Ply Snow)

New Tires - Jointed Concrete

A-weighted Sound Levels, dB

Microphone

Location, ft (m)

Nominal Speed, mph (km/hr)

50 1.0O.5J 50 1,00. 5J dO l9D.5i bu lyooJ iU \\.Ld-.'o) f-u (,11^. d;

25 (T.6)

50 (15.2)

76. U T6.U T9.2 TS.U 82. U 8i.2

T2.U T1.6 T3.0 Ti^.8 11 M 11.2

Worn Tires - Joii

A-weighted Sound

ated Concrete

Levels , dB

Microphone

Location, ft (m)

Nominal Speed, mph (km/hr)

50 (80.5) 50 (80.5) 6o (96.5) 6o (96.5) TO (112.6) TO (112.6)

25 (T.6)

50 (15.2)

77.8 78.2 81. i+ 82.8 81. U 81.0

73.8 73.6 76. i+ 76. i4 76.0 76.6

New Tires - Asphalt

A-weighted Sound Levels , dE

Microphone

Location, ft (m)

Nominal Speed, mph (km/hr)

50 (80.5) 50 (80.5) 60 (96.5) 60 (96.5) TO (112.6) TO (112.6)

25 (T.6)

50 (15.2)

T6.2 T6.2 T8.0 T8.8 No Data

T1.6 TO. 6 T3.^ TU.8 No Data

Worn Tires - Asphalt

A-weighted Sound Levels , dB

Microphone

Location, ft (m)

Nominal Speed, mph (km/hr)

50 (80.5) 50 (80.5) 60 (96.5) 60 (96.5) TO (112.6) TO (112.6)

25 (T.6)

50 (15.2)

TT.2 T6.8 80.2 80.8 No Data

T2.8 12. k T5.2 T^.2 No Data

New Tires - Continuous Poured Reinforced Concrete

A-weighted Soimd Levels , dB

Microphone

Location, ft (m)

Nominal Speed, mph (km/hr)

50 (80.5) 50 (80.5) 60 (96.5) 60 (96.5) TO (112.6) TO (112.6)

25 (T.6)

50 (15.2)

T9.8 79.8 82. U 83.0 86.2 Ql .h

12.6 13.6 ll.h ll.k 80.1+ 81.6

Worn Tires - Continuous Poured Reinforced Concrete

A-weighted Sound Levels , dB

Microphone

Location, ft (m)

Nominal Speed, mph (km/hr)

50 (80.5) 50 (80.5) 60 (96.5) 60 (96.5) TO (112.6) TO (112.6)

25 (T.6)

50 (15.2)

Ql.k 83.2 8U.6 86.0 86.8 8T.0

77.2 75.0 79.0 79.2 81.6 80.6

63
Figure A-6. Characteristic tread element pattern of tire-G (bias-ply studded

snow). The nominal new tread depth for this tire was 13/32 inch.

Shore hardness values ranging from 55-60 were observed with the

average being 58- The nominal worn tread depth for this tire was 6/32 inch and the Shore hardness values ranged from 60-62 with the

average being 6l.

6h
Tire G (Bias-Ply Studded Snow)

New Tires - Jointed Concrete

A-weighted Sound Levels , dB

Microphone

Location, ft (m)

Nominal Speed, mph (km/hr)

50 (80.5) 50 (80.5) 6o (96.5) 6o (96.5) 70 (112.6) 70 (112.6)

25 (7.6)

50 (15.2)

79. U 79.0 82.8 81.0 8k. 2 85.

U

7U.6 lh.6 11.0 76.2 81.0 79.8

Worn Tires - Jointed Concrete

A-weighted Sound Levels , dB

Microphone

Location, ft (m)

Nominal Speed, mph (km/hr)

50 (80.5) 50 (80.5) 60 (96.5) 60 (96.5) 70 (112.6) 70 (112.6)

25 (7.6)

50 (15.2)

79. U 81.^ 86.6 85.8 87.6 87.

U

75.8 75.6 81.0 80. h 83. h 83.

h

New Tires - Asphalt ' A-weighted Sound Levels , dB

Microphone

Location, ft (m)

Nominal Speed, mph (km/hr)

50 (80.5) 50 (80.5) 60 (96.5) 60 (96.5) 70 (112.6) 70 (112.6)

25 (7.6)

50 (15.2)

79. 1| 79.0 81. h 82.2 83.8 85.

U

lh.2 lh.6 11. h 11.0 79.0 79-6

Worn Tires - Asphalt

A-weighted Sound Levels , dB

Microphone

Location, ft (m)

Nominal Speed, mph (km/hr)

50 (80.5) 50 (80.5) 60 (96.5) 60 (96.5) 70 (112.6) 70 (112.6)

25 (7.6)

50 (15.2)

79.8 79.6 81.U 8^.-0 8h.O 85.8

7I1.8 15. h 11.2 78.0 81.0 81.1+

New Tires - Continuous PoTored Reinforced Concrete

A-weighted Sound Levels , dB

Microphone

Location, ft (m)

Nominal Speed, mph (km/hr)

50 (80.5) 50 (80.5) 60 (96.5) 60 (96.5) 70 (112.6) 70 (112.6)

25 (7.6)

50 (15.2)

79.6 80.2 82.8 83.2 87.8 86.2

7U.6 lh.6 18. h 11.6 81.6 81.0

Worn Tires - Continuous Poured Reinforced Concrete

A-weighted Sound Levels , dB

Microphone

Location, ft (m)

Nominal Speed, mph (km/hr)

50 (80.5) 50 (80.5) 60 (96.5) 60 (96.5) 70 (112.6) 70 (112.6)

25 (7.6)

50 (15.2)

82.2 82.1+ 85.0 85.6 87.2 87.0

75.0 15. h 78.8 79.2 82.8 82.6

65
Figure A-T. Characteristic tread element pattern of tire-BR (bias-ply rib

retread). The nominal new tread depth for this tire vas 10/32 inch.

Shore hardness values ranging from 5T-6l were observed with the

average being 59-

66
Tire BR (Bias-Ply Rit Retread)

Nev Tires - Jointed Concrete

A-weighted Sound Levels, dB

Microphone

Location, ft (m)

Nominal Speed, mph (km/hr)

50 (80.5) 50 (80.5) 60 (96.5) 60 (96.5) 70 (112.6) 70 (112.6)

25 (7.6)

50 (15.2)

70.8 72.6 7^.8 7^.2 77.0 77.6

65.8 67.0 71.0 70.1+ 71.6 72.

U

New Tires - Asphalt

A-weighted Sound Levels , dB

Microphone

Location, ft (m)

Nominal Speed, mph (km/hr)

50 (80.5) 50 (80.5) 60 (96.5) 60 (96.5) 70 (112.6) 70 (112.6)

25 (7.6)

50 (15.2)

73.8 lh.6 77.2 76. U 78.6 79.0

68..U 68.2 72.8 70.0 73.2 73. i+

New Tires - Continuous Poured Reinforced Concrete

A-weighted Sound Levels , dB

Microphone

Location, ft (m)

Nominal Speed, mph (km/hr)

50 (80.5) 50 (80.5) 60 (96.5) 60 (96.5) 70 (112.6) 70 (112.6)

25 (7.6)

50 (15.2)

79.8 80.0 83.0 83.8 85.8 86.

U

73. U 73.^ 76.6 77.0 79.8 78.8

67
Figure A-8. Characteristic tread element pattern of tire-RR (radial rib

retread). The nominal new tread depth for this tire was 10/32

inch. Shore hardness values ranging from 59-60 were observed

with the average being 59-

68
Tire RR (Radial Ri"b Retread)

New Tires - Jointed Concrete

A-veighted Sound Levels , d5

1 Microphone

Location, ft {zz)

Nominal Speed, mph (km/hr)

50 (50.5) 50 ^50.5' 6o (96.5) 60 (96.5) 70 (112.6) 70 (112.6)

25 (7.6)

50 (15.2)

72.6 11. k 73.6 Ik. 8 77.0 76.2

67.6 67.2 69.8 70.0 72.0 71.8

Ivev Tires - Aspha±x

A-veighted Sotmd Levels , dB

Microphone

Location, ft (n)

i.oEinal Speed, npn (km/hr)

50 (80.5) 50 (80.5) 60 (96.5") 60 (96.5) 70 (112.6) 70 (112.6)

25 (7- 6}

50 (15.2)

^2.- "2.0 76.0 74.5 76.2 75.6

66.- 66. 70.6 69.2 72.6 72. li

Nev Tires - Continucus rcs^ez. Reinforced Concrete

A-veighted Sound Levels , 13

Microphone

Location, ft (n)

lominal Speed, mph (im/hr)

50 (80.5) 50 (80.5) 60 (96.5") 60 (96.5) 70 (112.6) 70 (112.6)

25 (7.6)

50 (15.2)

78.6 77.8 80.6 82.0 83.0 83.6

72.6 ^2.2 76.2 75.8 "^.2 76.2

69
5 . Appendix B

Instrument Descriptions

Unless otherwise stated, all instruments are Briiel and Kjaer^'''.

Type UA 0207 Windscreen : When a microphone is exposed to wind, and wind velocit

variations, the turhulence created around the microphone cause a noise

to be generated due to a variation of air pressure on the diaphragm. To

reduce this extraneous "wind noise, a spherical windscreen constructed

of specially prepared porous polyurethane sponge was utilized.

Type U22O Pistonphone : This instrument is a small, battery-operated precision

sound source which provides quick and accurate direct calibration of

sound measuring equipment. When fitted to a B & K microphone, the pistonphone produces a sound pressure level of 12k +0.2 dB, re 20 yPa, at a frequency of 250 Hz +1% (controlled by means of a transistor circuit).

Maximum stability and a very low distortion (less than 3% at 250 Hz)

result from the piston arrangement consisting of two pistons moving in

opposite phase. The calibration of the pistonphone is performed at normal

atmospheric pressure. Ambient pressure corrections are necessary for

pressures other than T60 mm Hg. This calibration is not influenced by

relative humidities up to 100^ or temperatures within the range of 0 - 60°i

(32 - lJ40°F).

Microphone : When one speaks of a microphone, a three part minimum system is

implied: (l) a protecting grid; (2) a condenser microphone cartridge;

and (3) a microphone preamplifier or cathode follower. For this testing the following components were utilized.

Type U161 One-inch Condenser Microphones : The one-inch free-field con- denser microphone is a type possessing relatively high sensitivity and

covering a range of applicability from 2 Hz to I8 kHz (frequency range)

and 15 dB to ihO dB (dynamic range). A feature of these microphones is

long-term stability under a variety of environmental conditions and

insensitivity to temperature variations. Condenser microphones, in

addition, were chosen because of their higher dynamic range, ease in

calibration, and uniform frequency response. The cartridge which houses

the microphone diaphragm is protected by the grid on one side and on the

other is normally screwed onto the preamplifier. This particular microphone vents into a dehumidifier (which is located between the microphone

and the preamplifier) rather than air. The silica gel drys the air used

by the microphone for pressure equalization.

Commercial instr-uments are identified in this report in order to adequately

specify the experimental procediire. In no case does such identification

imply recommendation or endorsement by the National Bureau of Standards , nor does it imply that the equipment identified is necessarily the best available

for the purpose.

TO
Type UA 0310 Dehutnidifier : The dehumidifier is designed to be mounted

between the ^l6l condenser microphone and its amplifier. It contains

silica gel to dry the air used by the microphone for pressure equalization. When used in 100^ relative humidity situations, the silica gel

requires drying approximately once a month. The drying is accomplished

by heating the silica gel for some hours at a temperature of 100°C.

Type 2619 Half-inch FET Preamplifier : This preamplifier featiures a very

high input impedance field-effect transistor, which represents virtually

no load to the microphone cartridge. To mate the 2619 with the ^l6l a suitable adapter must be utilized (model DB-03T5).

Built into the preamplifier itself is a 6.3V heating coil to prevent

condensation when operation must be carried out in cold or humid environments .

The above described microphone subassembly provides reliable operation

over a wide range of temperature, humidity, and vibration and allows

precision sound pressure measurements to be made over a wide frequency

and dynamic range.

Type 280^1 Two Channel Power Supply : This unit is a portable, batterydriven supply unit designed to provide the necessary polarization

voltage for condenser microphones and their accompanying preamplifiers .

NBS Field Instrumentation : To facilitate data acquisition in the field, this

battery-powered instriomentation system was designed and fabricated by

NBS specifically for application to passby noise measurements. The

\mit contains a 60 dB variable gain amplifier which provides the needed

signal conditioning (amplification/attenuation) prior to recording. In

addition to recording the signal, weighting networks and hold circuitry

are included to allow for direct reading of the linear and A-weighted

fast response sound level observed during the passby. The hold circuitry

and weighting networks meet the Type 1 requirements for the fast dynamic

characteristic and the A-weighting response respectively of American

National Standard Specification for So\md Level Meters, Sl.i+-19T1. The

linear hold circuitry provides an indication as to whether or not a tape

channel had become saturated (i.e., the signal had exceeded the dynamic

range of the recorder) and thus the data were not acceptable. The

A-weighted hold circuitry allowed for direct reading of the A-weighted

sound level observed during a passby without the necessity for

returning the tape recordings to the laboratory for reduction and

analysis

.

Nagra Model SJ Tape Recorder : This unit is a portable 3-track (l/U inch

magnetic) tape recorder with two high quality amplitude modulated sound

tracks (25 Hz to 35 kHz), plus a third FM track for recording very low

frequencies (dc to k kHz), commentary, synchronization signals or timing

information. The instrument records and reproduces at four speeds —

71
15, 7-1/2, 3-3/^, and 1-1/2 ips . The two-amplitude modulated channels

can be fed from separate microphone inputs. The volume is controlled by

separate step attenuators.

Type 33^7 Real Time Analyzer : The real time analyzer is composed of two

basic units: (l) type 2130 frequency analyzer and (2) type i4710 con- trol and display unit.

The 2130 contains a measuring amplifier, filter channels "with 1/3-octave

bandwidth, a linear channel, weighting channels, true RMS detectors, and

the synchronization system for scanning the channels.

The analyzer contains 38 parallel channels. 33 of these channels contain

1/3-octave filters with center frequencies from 12.5 Hz to 20 kHz. The

remaining five cha,nnels are reserved for the four weighting network

filters — A, B, C, and D — and one linear response channel.

The U7IO contains the circuitry for the 12-inch cathode ray tube (CRT),

the Nixie displays, digital readout, and the logic control. The logic

control section controls the analog/ digital conversion and the communication sequence for external systems, as well as the internal synchronization in the 33^7 during display or read-out modes.

The level in each channel can be read in dB directly on the screen, while

a Nixie display shows the output level of any selected channel. This

channel is indicated on "che CRT as a brighter trace. The complete channel

display is renewed every 20 msec.

Outputs are provided for both analog instriiments (X-Y or level recorders)

as well as digital (on-line computer or tape pimcher) . The digital output

is in binary coded decimal (BCD) code.

Time constants may be selected from 20 msec to 20 sec so that confidence

limits can be maintained throiighout the frequency range.

Model 70U Raytheon Computer System : The Raytheon 70U computer system is a general purpose digital system that provides a l6-bit central processor

unit with 900 nanosecond cycle time for on-line, real time applications.

The hardware configuration includes an 16K (expandable to 32K) memory system, direct input/output bus, automatic priority interrupt, direct and

indexed addressing, and byte and word addressing and instructions.

Standard peripherals such as high speed paper tape, ASR-33 teletype,

card equipment, and a magnetic tape unit are also included.

72
6. References

[I] Anon., Truck Noise-1, Peak A-Weighted Sotind Levels Due to Truck

Tires, U. S. Department of Transportation Report OST-ONA-Tl-9

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

[2] Tetlov, D., Truck Tire Noise, Sound and Vibration, 5.(8), 17-23

(1971).

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

Addendum to Truck Noise-1, Peak A-Weighted Sound Levels Due to Truck

Tires, U. S. Department of Transportation Report OST/TST-72-1

(National Bureau of Standards, Washington, D. C, 1972).

[k] Leasure, W. A., Jr., and Mathews, D. E., Pecos Truck Tire Noise

Study: A Suimnary of Results, NBSIR 'Jk-hk6, National Bureau of

Standards, Washington, D. C. (197^).

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

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

of Transportation Report DOT-TST-TU-21 (National Bureau of Standards,

Washington, D. C, 197^).

[6] Leasure, W. A., Jr. and Corley, D. M. , Truck Noise 1-B, Spectral and

Directional Characteristics of Noise Generated by Truck Tires, U. S.

Department of Transportation Report DOT-TST-T5-71 (National Bureau of

Standards, Washington, D. C, 1975).

[7] Leasure, W. A., Jr., Automobile Tire Noise: A Review of the Open

Literature, Proceedings of Noise-Con 73, Washington, D. C, 187-195

(1973).

[8] Hillquist, R. K. and Carpenter, P. C, A Basic Study of Automobile

Tire Noise, Sound and Vibration, 8_(2), 26-28, (197^)-

[9] Richards, M. G., Automobile Tire Noise - A Comprehensive Study, Sound

and Vibration, 8(5), h2-kl (197^)-

[10] Veres, R. E. , Tire Noise Investigation and Test Methods, Technical

Report No. CRR 7^-6 (Ford Motor Company, Dearborn, Michigan 197^)-

[II] American Society for Testing and Materials, D22kO-6Q, Standard Method

of Test for Indentation Hardness of Rubber and Plastics by Means of a Dijrometer in Part 37, Book of ASTM Standards (American Society for

Testing and Materials, Philadelphia, Pennsylvania, 197^).

[12] Potts, G. R., Application of Holography to the Study of Tire

Vibration, Tire Science and Technology, TSTCA, l(3), 255-266 (l973).

73
[13] Yurkovski, B. , Astrov, V. A., and Ivanteev, A. V. , The Influence of

Design Parameters on the Shock-Ahsorbing Capacity, Road-Handling, and

Noise Level of Car Tyres (in Russian), Kauchuck i Rezina 26( 3 ) ? 30-33

(1967).

[ik] Wiener, F. M. , Experimental Study of the Airborne Noise Generated by

Passenger Automobile Tires, Noise Control 6_(U), 13-l6 (1960) .

[15] Engler, G. , Factors Contributing to Wheel Noise (in German), Kraft fahrzeug'

Technik lji(l2), ^1+3-^+36 (196^+).

[16] Rathe, E. J., Traffic Noise: The Influence of Road Surface and Traffic

Volume, presented at the Thirteenth World Congress of the Road, Tokyo,

Japan (196T).

[17] Waters, P. E., Commercial Vehicle Rolling Noise, Institute of Sound and

Vibration Research Memorandum No. 3595 University of Southampton,

Southampton, England (l970).

Ik
Acknowle dgement s

The authors -would like to recognize the contributions made "by the

following organizations which have greatly aided this program: the

Pennsylvania Department of Transportation especially Mr. Wade Gramling and

the staff of the Wallops Station facility of the National Aeronautics and

Space Administration. Special thanks go to our liaison at Wallops Station,

Mr. G. Godwin.

The authors also express appreciation to Mr. W. J. Rinkenen for his

assistance in data acquisition and reduction, to Mrs. J. Russell for the

typing and preparation of the manuscript, and to Mr. W. H. Close (Office

of Noise Abatement, U. S. Department of Transportation) for his review and

comments

.

75
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