iPORT NO. DOT-TST-76T-5

TRUCK NOISE 1-D

EMPIRICAL MODEL FOR PREDICTING IN-SERVICE

TRUCK TIRE NOISE LEVELS

OF TJf^y^,

FINAL REPORT

JULY 1976

AVAILABILITY IS UNLIMITED. DOCUMENT HAS BEEN

RELEASED TO THE NATIONAL TECHNICAL INFORMATION

SERVICE, OPERATIONS DIVISION, SPRINGFIELD,

VIRGINIA, 22161, FOR SALE TO THE PUBLIC.

U.S. DEPARTMENT OF TRANSPORTATION

OFFICE OF THE SECRETARY

Office of Noise Abatement

Washington, D.C. 20590
This document is disseminated under the sponsorship

of the Department of Transportation in the interest

of information exchange. This document does not

constitute an official statement of policy or standard. The United States Government assumes no liability for its contents or use thereof. Specific

commercial products are identified in this report in

order to adequately specify the tasks performed. In no case does such identification imply recommendation

or endorsement by the Department of Transportation.

Kilmer, R. D. , Leasure, W. A., Jr., Corley

D. M., Mathews, D. E., Snoemaker, C. 0.

' Jr., Truck: Noise 1-D: Empirical Model

' for Predicting In-Service Truck Tire Noise

Levels, Report No. DOT-TST-76T-5,

6t) pages (Available from the National

Technical Information Service, Springfield, VA, 22161, Jul;^ 1976).

200

2 7
TECHNICAL REPORT STANDARD TITLE PAGE

1. Report No. DOT-TST-76T-5

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

4. Title and Subtitle Truck Noise I-D

Empirical Model for Predicting In-Service

Truck Tire Noise Levels

5. R"»port Date July 1976

6. Performing Organization Code

7. Author(s) R. D. Kilmer, W. A. Leasure, Jr., D. M. Corley,

D. E. Mathews, C. 0. Shoemaker, Jr.

,8. Performing Organization Report No.

9. Performing Organization Name and Address National Bureau of Standards

Department of Commerce

Waricioiixii^ -i n a1-nn uuii , Du . C\j , ^.yj^oH ?n9'^4

10. Work Unit No.

11. Contract or Grant No. DOT-AS-10004

13. Type of Report and Period Covered

Final

^ 12. Sponsoring Agency Name and Address U. S. Department of Transportation

Office of the SecretaryOffice of Noise Abatement

Washington, D. C. 20590

14. Sponsoring Agency Code

15. Supplementary Notes

16. Abstract

SAE Recommended Practice J57 -- Sound Level of Highway Truck Tires -- specifies

a simple, practical noise certification test procedure for tires which results

in a single-number rating -- maximum A-weighted sound level -- of the coastby

sound level measured according to prescribed procedures. Such a rating by

itself, however, does not allow prediction of in-service noise levels. This

report discusses the basic assumptions and necessary input data for a DOT/NBS

developed empirical model which utilizes the certification test results to

predict in-service noise levels. The usefulness and expected accuracy of the

predictive model are shown through a comparison of measured versus predicted

maximum A-weighted sound levels for a variety of truck/tire combinations.

17. Key Words 18. Distribution Stotement Acoustics; noise measurement; noise Availability is unlimited. Document

(sound); tire noise; transportation may be released to the National Technical

noise; truck. Information Service, Operations Division,

Springfield, VA 22161, for sale to the

public

.

19. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No. of Pages 22. Price UNCLASSIFIED UNCLASSIFIED 62

Form DOT F 1700.7 (8-69)
I
Table of Contents

Page

Abstract ii

1. Introduction 1

2. Feasibility Study .... 2

3. Model Validation Program 8

3.1 Field Test Site 8

3.2 Test Tires 10

3.3 Test Vehicles 13

3.U Test Procedure l8

k. Results of F\ill-Scale Validation Program 26

5. Application of Predictive Model h2

6. Appendix A. Model Computational Procedures ....

6.1 General Assumptions of the Model UT

6.2 Example Com.putation Using the Model 50

T. Appendix B. SAG J5T 59

8. References 6l

Acknowledgements 62

i
Abstract

SAE Reconimeruied Practice J5T — Sound Level of Highway Truck Tires —

specifies a simple, practical noise certification test procedure for tires

which results in a single-number rating -- maximum A-weighted sound level —

of the coastby sound level measijred according to prescribed procedures. Such

a rating by itself, however, does not allow prediction of in-service noise

levels. This report discusses the basic assumptions and necessary input data

for a DOT/KBS developed empirical model which utilizes the certification test

results to predict in-service tire noise levels. The usefulness and expected

accuracy of the predictive model are shown through a comparison of measured

versus predicted maxim-am A-weighted so\and levels for a variety of truck/tire

combinations

.

ii
1 . Introduction

Initial interest in truck noise can be traced to the early 1950' s; however, in the test procedures developed by industry and the Society of

Automotive Engineers (SAE) for the measurement of exterior truck noise, the

speed of the vehicle under test vas maintained below 35 mph (56.3 km/hr) in

order to limit^ the noise contribution of the tires. The first input to the

open literature that identified the relative contributions of tire noise to

total truck noise was a report published in 196k which documented tests

conducted by the American Trucking Associations, Inc.[l]— . On the basis of

this study, industry data, and subsequent studies — principally those by the

Rubber Manufacturers Association— and General Motors [U] — the SAE Vehicle

Sound Level Committee established a Truck Tire Noise Subcommittee charged

with developing a test procediore and a recommended maximum sound level for

truck tires consistent with the SAE recommended practice for maximum exterior

sound levels of heavy duty trucks and buses. At essentially the same time,

the Department of Transportation initiated a wide ranging study of tire noise

variables through an interagency agreement with the National Bureau of

Standards. An extensive series of truck tire noise tests were conducted at

Wallops Island, Virginia during 1970 and 19Tl[5 56].

The Truck Tire Noise Subcommittee — composed of personnel from tire

manufacturers, auto and truck manufacturers, and government — accumulated a wide variety of test results (both objective and subjective data) and on this

basis formulated a test procedure applicable to highway truck tires which

they felt was adequate for their piarposes; namely, "qualification of tires

for radiated sound levels by (tire) manufacturers and recappers" [3] . They

realized that many issues were not resolved and that further research, was

necessary to address the remaining issues; however, they also realized that

the need for a standard precluded further delay. Therefore, SAE Recommended

Practice JST — Sound Level of Highway Truck Tires — was approved and issued

in 19T3[T]~ . This standard specifies a simple, practical noise

certification test procedure for tires which results in a single-number

rating — maximum A-weighted sound level — of the coastby sound level

measured according to prescribed procedures. Such a rating by its-elf,

however, does not allow the prediction of in-service noise levels. For this

reason, a predictive scheme which allows one to utilize the certification

test results to predict in-service noise levels is needed. Utilizing the

extensive Wallops Island truck tire noise data base, which was developed

following procedures essentially identical to SAE J5T—' , DOT/NBS developed a simple empirical model to satisfy this need.

— Figures in brackets refer to references at the end of this- report.,

2/— The data obtained in this study were never published, however, the results^ are summarized in references [2,3].

3/ — The complete text of SAE J5T is reproduced in Appendix B.

-^The DOT/NBS data were obtained utilizing "fasi:" meter respons-e while SAR JJ'T specifies use of "slow" meter response.
The "basic assumptions and necessary data for application of the model

are as follows:

(1) The necessary input data are A-veighted sound level versus time

data -which can "be converted to A-veighted sound level versus

distance data. Such data are relatively simple to acquire without

the necessity for extensive instrumentation.

(2) The basic assumptions are:

The data for a given axle can be represented by the

certification data assuming (a) the number of tires mounted

on the axle, (b) the tread design, and (c) the state of tread

.wear of the tires are comparable.

For vehicles with numerous axles and axle locations, the

certification data representative of each axle (a) can be

adjusted to account for load differences (between

certification and in-service), (b) can be shifted spatially

according to the geometric arrangement of the axles of the

particular vehicle of interest, and (c) can be added together

on an energy basis.

In the remainder of this report the usefi^Lness and expected accuracy of

the predictive model is shown through a comparison of measured versus

predicted maximum A-weighted sound levels for a variety of truck/tire

combinations. Application of the model is illustrated by means of an example computation in Appendix A.

2. Feasibility Study

In order to test^the hypothesis of the predictive model, the DOT/NBS

single-chassis [h x 2— ] Wallops Island data[5 5 6] were used to predict the

maximum A-weighted sound level and the A-weighted sound level versus

distance data for seventy-six (T6) test conditions which corresponded to runs actually made with a 6 x U tractor with a double-axle trailer [6 x h

DAT]. This was the only vehicle configuration that could be tested on the

basis of the Wallops Island data.

These seventy-six conditions corresponded to coastbys at vehicle speeds

ranging from 25 to 60 mph (^+0.2 to 96.6 km/hr) . [The test matrix called for

test runs to be made in 5 mph (8.0 km/hr) increments from 30 to 60 mph (U8.3

to 96.6 km/hr).] Nine new and retreaded tires of various tread designs —

four ribs, four cross-bars and one pocket tread — were tested.

— The nomenclature U x 2 relates to the number of wheel positions — U, and

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

of tires — 6. Therefore, a 6 x U would have 10 tires mounted at 6 wheel

positions, h of which are driven.

2
Before the rav tire noise data could be utilized as input to the model,

it was necessary to correct the A-weighted sound level versus distance data

for any given axle to account for any differences which existed between the

loading conditions for^the 6 x U tractor with double-axle trailer and the

single-chassis vehicle— . The load-corrected h x 2 single-chassis data were

then utilized to predict the noise levels corresponding to the actual test

runs of the 6 x h tractor with double-axle trailer.

The results of the feasibility study are listed in Table 1. The trial

numbers listed in the table refer to the tractor-trailer test matrix

utilized in the DOT/NBS truck tire noise study! 5, 6^]. It should be noted

that only data measured at 50 feet (l5.2m) for test rims on the concrete

surface were used in this feasibility study.

A graphical comparison of the measured versus the predicted maximum

A-weighted sound levels is presented in Figure 1. A band of +h dB on the

line would encompass 90 percent of the data points. A recheck of some of

the individual data points for which there was the greatest discrepancy

between the measured and calculated values revealed that many of these data

points were out of character when compared with the data points at vehicle

speeds lower and higher than the datum point at 50 mph (80.5 km/hr) — i.e.,

individual datum points deviated significantly from the expected approximate

ho log V relationship between noise level and vehicle speed. The danger of

utilizing the data for a single test run to establish the noise level

corresponding to a given vehicle speed is pointed out by this exercise.

As further evidence of the validity of the model, comparisons are presented (Figures 2 and 3) between the A-weighted sound level versus

distance data predicted by the model and those actually measured for two of

the seventy-six conditions. These particular conditions were selected to

test the capability of the model to predict acciirately the shape of the

A-weighted soiind level versus distance curve. In one case the difference

between the predicted and measured maximum A-weighted sound level was small

(approximately 0.6 dB), while in the other case the difference was quite

large (approximately 5.3 dB). It is clear from the data that the model

predicts the shape of the A-weighted sound level versus distance (or time)

ciirve very well, even for those cases where the maximum A-weighted sound

level is not as well predicted.

—Very little data on the effect of load on tire noise levels are published

in the literature. The data that are available deal only with selected

tires — a circumferential rib, one typical continuous rib, one typical

cross-bar and one type of pocket tread -- and only two loading conditions — loaded, 17,720 pounds per axle (8038 kg per axle); and unloaded, 6l20

pounds per axle (2776 kg per axle) [556]. In this current study it is

assumed that the noise level changes linearly with load and that any

rib or cross-bar tire behaves with load changes exactly like the typical

rib and cross-bar for which data exist. The load corrections are determined from Figure A-1 which is a plot of maximum A-weighted soiind

level versus load difference (certification loading minus in-service

loading) for the typical rib and cross-bar tires.

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MEASURED A-WEI6HTED SOUND LEVEL, dB ri20^Pa

Figure 1. Comparison of the calculated and measured maximum A-weighted sound

levels at 50 feet (15.2 m) for the seventy-six test conditions

corresponding to runs of a 6 x U tractor with double-axle trailer.

These data were obtained in a previous DOT/NBS truck tire noise

study [5,6].

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The results of this feasibility study were very encouraging considering

the a priori- known deficiencies associated with the model and/or input data

available ; namely

The comparisons are based on a single test run.

The load corrections to be applied to the data are based on the

assumption that noise level increases linearly with load and that

all rib and cross-bar tires behave like the particular rib and

cross-bar tire for which load data exist.

The input data obtained from the noise certification test includes

a contribution from the steering tires. This noise contribution

which gets added in every time an additional axle is added is not

accoTinted for in the model.

On the basis of the results of this feasibility study, the decision, was made to carry out a full scale test of the predictive model to serve as the

basis for validation and refinement.

3. Model Validation Program

The operational procedures and measurement/analysis instrumentation

utilized in this model validation program were similar to that used in

previous DOT/KBS 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.

3.1. Field Test Site

The dynamometer course at the U. S. Army Proving Qround located in

Yuma, Arizona was selected as the test site for the data acquisition phase

of the program. This facility provided an adequate stretch of pavement

necessary for safe operation of the test vehicles, a flat terrain providing

a well-defined reflecting surface without any unusual reflection or attenuation effects, a remote location where interference from other noise

sources could easily be avoided and normal climatic conditions- — low

relative humidity and very infrequent rainfall — Ideal for the eJfi'cient

conduct of outdoor testing. Utilization of this site was arranged through

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

Ground, Aberdeen, Maryland.

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

foot (152. U m) radius turn-arounds at each end. The roadway is 30 feet CP.l

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

asphalt. A 6OO foot (I82.9 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 k shows an overall view of the test site with the location of the test section and

maintenance facilities noted.

8
Figure k. Plan of dynamometer coiirse at the U. S. Army Yuma Proving Ground,

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

9
To comply with the measTirement area requirements of SAE J57 (see Appendix

B), an asphalt pad "was constructed adjacent to the dynamometer course roadway.

This triangular-shaped pad consisted of three rectangular sections of asphalt

each 3 inches (T.6 cm) thick, 10 feet (3.0 m) wide and 600, kOO, and 200 feet

(182. 9 J 121.9, and 61.O m) long, respectively. The pad was allowed to cure

for two weeks after construction and then was sealed using a commercial

driveway sealer. Figure 5 is a photograph showing the test section on the

dynamometer coiirse roadway and the measurement area pad.

3.2. Test Tires

For this study a sample of five tire types were selected for evaluation.

The tires were all size 11.00-2^.5 and were of the following construction,

state of wear and tread design:

Tire A New bias ply rib

Tire B New bias ply rib

Tire C New steel belted rib

radial ply

Tire D Half-worn bias ply cross-bar

Tire E Half-worn bias ply cross-bar

The test tires were always mounted on the drive axle(s) of the tractors. Rib

tires (tire C) whose characteristic tire noise level was known to be low were

mounted on the steering axle. The trailer tires utilized during testing were

those which were on the trailer when it was rented. These tires were bias ply

rib type tires with three different tread designs (designated Rl, R2 and R3).

The characteristic tread patterns for the steering, test and trailer

tires arg, shown in Figure 6. The nominal tread depth— and average Shore

hardness— for these tires are also indicated.

— Tread depth measurements were taken at four equally 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.

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

D22U0-68[8]. 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

.

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TIRE A TIRE B

Nev Bias Ply Rib

Average Shore Hardness - 60 i^iyKOfi Average Shore Hardness - 5^

19 Nominal Tread Depth - inch ;K(>)-1 Nominal Tread Depth - — inch

TIRE C TIRE D

I

TIRE E

New Steel Belted Radial Ply Rib

I I Nominal Tread Depth inch

Average Shore Hardness - 60

Half-Worn Bias Ply Cross-Bar

Nominal Tread Depth - inch

Average Shore Hardness - Gh

TIRE Rl

Half-Worn Bias Ply Cross-Bar

11 ^ Nominal Tread Depth - — inch

-sX^" Average Shore Hardness - Gh

Half-Worn Bias Ply Rib

13 Nominal Tread Depth - — inch

Average Shore Hardness - 63

TIRE R2 TIRE R3

Half-Worn Bias Ply Rib

g Nominal Tread Depth - inch

Average Shore Hardness - TO

Half-Worn Bias Ply Rib Retread

Nominal Tread Depth - inch

Average Shore Hardness - 58

Figure 6. Characteristic tread element pattern, nominal tread depth- and

average Shore hardness for the steering, test and trailer tires.

12
In accordance with standard operating procedure for bias-ply tire use the

tires utilized during this test program "were not "balanced. When nev tires are installed on a truck, balancing is not performed unless there is a definite

handling problem or severe vibration reported "which might jeopardize the

safety of the vehicle. When such a problem arises, the entire front end

assembly, not just the tires, is checked. Unlike the normal practice "with

automobile tires, only front (steering) tires are ever balanced on trucks.

A tire "was not considered acceptable as a test specimen for the tire

noise investigation until it had "undergone a break-in period of sufficient

mileage under actual driving conditions to ens"ure the removal of all mold

marks and manufacturing irreg"uLarities . Immediately prior to the actual noise

testing of a given set of tires, a "warm-up proced"ure "was followed which

normally required a minim"um trip of approximately 10 miles (,l6.1 km).

3.3. Test Vehicles

Six different single-chassis and tractor-trailer combinations were

utilized throughout this program. Two tractors — a U x 2 and a 6 x U —

served as the basic single- chassis (or straight truck) test vehicles,

hereafter noted as U x 2 STR and 6 x h STR, respectively. The k x 2 tractor

was also tested in combination with a single-axle trailer {h x 2 SAT), a double-axle trailer {h x 2 DAT), and a double bottom {k x 2 DB). The 6 x h

tractor was tested in combination with a double-axle trailer {6 x h DAT).

Overall views of these test vehicles and the loading arrangements are shown in

Figures 7 through 9-

The h X 2 and 6 x U test vehicles were International—'^ Model CO-UOTOA

single drive axle tractor and International Model COF-UOTOA dual drive axle

tractor, respectively. Both tractors were equipped with 10 hole Budd wheels,

II.OO-2U.5 tires, a 350 CID C"ammins diesel engine and a lO-speed transmission.

Three trailers -- two single-axle trailers and one double-axle trailer —

were used in this study. The single-axle trailer was the front trailer of the

double bottom combination which consisted of two 27 foot (8.2 m) flat bed

trailers interconnected by a dolly. These trailers were equipped with 10 hole

Budd wheels and 11.00-2U.5 type Rl and R2 tires. The mounting locations of

these tires are shown in Figure 10. The double-axle trailer was a hO foot

(12.2 m) flat bed trailer equipped with 10 hole Budd wheels. Size 11.00-2U.5

type R3 tires were mounted at all axle positions.

—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.

13
U X 2 Straight (U x 2 STR)

^ X 2 Tractor with Single-Axle

Trailer x 2 SAT]

Figure 7- View of test vehicles used in model validation study.

11+
4x2 Tractor with Doutle-Axle Trailer (k x 2 DAT)

U X 2 Tractor "with Double Bottom Trailer x 2 DB)

Figure 8. View of test vehicles used in model validation study.

15
r

6 X h straight [6 x h STR)

r

6 X k Tractor with Double-Axle Trailer i6 x h DAT)

Figure 9. Viev of test vehicles used in model validation study.
1 TIREC

TEST TIRES

TIRE R1

TIRER1

TIRER2

TIRER1

Figure 10. Mounting location of tires on the h x 2 tractor vith double bottom

trailer

IT
The lineal dimensions between axles of the various vehicle configurations

are given in Table 2. These dimensions, required as input data for the

predictive model, establish the spatial location of the respective axles.

The vehicles vere operated in a loaded condition for all test runs. The

loading was provided by either a series of steel plates or concrete blocks as shown in Figures 7 through 9. The resulting weight distribution on each axle

and the gross vehicle weight or gross combination weight for each test

configuration are given in Table 3. These loading values, which were

representative of the allowable weight limits regulated by Federal law prior

to 197^ for vehicles in interstate transit, were: l8,000 pounds (8,l65 kg) on

a single axle, 32,000 po\mds (1^1,515 kg) on tandem axles and 73,280 pounds

(33,2U0 kg) total gross combination weight. The only exception to these

weight limits in the model validation study is in the case of the U x 2 double

bottom with a total gross combination weight of 71j597 pounds (32,^76 kg).

This lighter loading was used because of the load limit specified by the

manufactirrer of the double bottom.

The bias ply tires were inflated to 75 psi (5-2 x 10^ Pa) and the radial

ply tires to 80 psi (5-5 x 10 Pa). These inflation pressure/load values were equivalent to 75-90 percent of the rated tire load per Tire and Rim

Association recommendations.

In view of the newly adopted allowable weight limits—'^, a limited

investigation was carried out with increased vehicle loading. Table h lists

the vehicles and loadings studied. Only tire E was utilized and to

differentiate the two loading conditions the increased loading is denoted as E* . The increased loading was equivalent to 90-100 percent of the rated tire

load at 75 psi (5-2 x 10 Pa) per Tire and Rim Association recommendations.

3.^. Test Procedure

The test procedure utilized was essentially identical to that specified

in SAE J57; however, the following exceptions should be noted:

"Fast" meter response was utilized.

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

asphalt

.

—^The Federal-Aid Highway Act of 197^ revised Section 127 of Title 23 of the

United States Code to permit commercial vehicles to carry a maximum of

20,000 pounds (9,072 kg) on a single axle, 3^,000 pounds (15,^22 kg) on tandem axles and 80,000 pounds (36,288 kg) total gross combination weight.

These limits affect the interstate highway system but provide that any

state which allowed higher limits previous to July 1956 may continue those

limits in effect on the interstate system.

18
Table 2. Lineal dimensions in inches (meters) of the six

single-chassis and tractor-trailer combinations used

as test vehicles in this study. The dimensions a through e are defined in the sketches belov the

table.

Test Vehicle

Vehicle Dimensions, inciibs (m)

a b c d e

liM- XV- P£- '^T'R Dxn 118

(3.0)

li Y P c;Arr 118

(3.0)

233

(5.9)

li V- ? DAT 118

(3.0)

370

{9M

52

(1.3)

U X 2 DB 118

(3.0)

233

(5.9)

115

(2.9)

235

(6.0)

6x1+ STR

(3.7)

50

(1.3)

6 X U DAT Ihh

(3.7)

50

(1.3)

3U6

(8.8)

52

(1.3)

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21
The distance between the point of entrance and point of exit of the

test section vas 600 feet (182.9 m)

.

Measurements were made of both coast and powered passbys. A

constant speed was maintained during powered passby test runs.

The components of the data acquisition and recording instrumentation,

plus the automatic tape recorder control and elapsed time system utilized are shown in Figure 11.

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

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

laboratory for the 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 single point

calibration utilizing a pistonphone which produced a 12h 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 12 shows th^e. 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 13 identifiesthe eqioipment 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 instimcted —^^A pistonphone generates a reference sound pressure level of 12U dB Cre 20 yPa)

only at the standard atmospheric pressure of T6Q mm Hg. For ambient pressure

conditions other than standard the actual level will vary from the reference

value of 12k dB (e.g. , T60 + 10 mm Hg corresponds to 12h + 0.1 dB).

Because the magnitude of this departure from the reference level is small

for the range of ambient pressure conditions at the Yuma test site, no corrections were made to the data.

22
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25
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 vhich "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.

k. Results of Full-Scale Model Validation Study

In order to develop the data base necessary to evaluate the DOT/NBS tire

noise predictive model, the test matrix shown in Table 5 was established. The

data acquisition portion of the full-scale validation study followed this

pre-defined test plan.

The objective of the test program was to obtain two sets of data: (l) 50

mph (80.5 km/hr) coastby A-weighted sound Ij^^l versus time data for the h x 2

single-chassis vehicle (certification data)— to serve as input for the predictive model, and (2) 55 mph (88.5 km/hr) coastby and powered passby

A-weighted sound level versus time data for all of the single-chassis and

tractor-trailer combinations in the test to be used for comparison with the

model predictions. The maximum A-weighted soiond levels for all test vehicle

and tire combinations measured during the test are presented in Tables 6

through 12

.

Before.^the certification data could be used as input to the model, load

corrections— — to account for load differences between the U x 2 STR and

the other vehicle configurations -- were applied to these A-weighted sound

level versus time data. A speed correction was also applied to these data

using a hO log V relationship between sound level and vehicle speed.

Utilizing these adjusted data, the maximum A-weighted sound levels and

A-weighted sound levels versus distance were calculated for all test

conditions using the empirical model. [See Appendix A for an example of the

step by step computational proced\ares of the model.] To accoxmt for engine

noise when predicting in-service total truck noise, the engine was

approximated by an omnidirectional point source located on the center line of

the vehicle directly over the steering axle. The A-weighted sound pressure

level of the engine was assumed to be 80 dB at 50 feet (15-2 m) . The value of

80 dB was selected on the basis of a comparison of the calculated and measured

powered passby noise levels to determine the best "empirical fit" for the

data. — To obtain the necessary certification data for the trailer tires, these

tires were mounted on the h x 2 straight test vehicle in the same arrangement as on the trailers. The certification levels are given in Table 6

for tire Rl on the first trailer and dolly of the double bottom, the com- bination of tires Rl and R2 Cdenoted Rl,2) on the last trailer of the

double bottom, and tire R3 on the double-axle trailer. —13/See footnote 6. Th.e load corrections applied to these data were determined

from Fig\are A-1.

26
Table 5. Test matrix for DOT/NBS empirical truck tire noise

model validation study. O's correspond to input data

to the model and X's to data to be compared with the

model predictions. A minimum of tvo test runs were

made for each operational condition.

Test

Vehicle

-h X 2

STR

h X 2

STR

h X 2

SAT

1+ X 2

DAT

h X 2

DB

6 X h

STR

6 xh

DAT

Speed

,

mph (km/hr)

50

(80.5)

55

(88.5)

55

(88.5)

55

(88. 5)

55

(88.5)

55

(88.5)

55

(88.5)

Operational

Modet C p c p c p c p c p c p c p

T

E

S

T

T

IR

E

C

0

D

E

A 0 X X X X X X X X X X X X

B 0 X X X X X X X X X X X X

C 0 X X X X X X X X X X X X

D 0 X X X X X X X X X X X X

E 0 X X X X X X X X X X X X

E* 0 X X X X X X X X

Rl 0

Rl,2 0

R3 0

C - Passby in coast mode

P - Passby in power mode

27
Table 6. Maximum A-veighted sound levels, as measured at 50 feet (l5.2 m) , for

the k X 2 straight test vehicle operated in the coast mode at a nominal speed of 50 mph (80.5 km/hr) [certification test runs]. These

data are adjusted to 50 mph (80.5 km/hr) using a hO log V relationship "between sound level and vehicle speed.

Test Tire Test Run Actual Speed Maximum A-Weighted Sound Level, dB re 20 yPa

Code Number mph (,km/hrj MeasTored Adjusted to 50 mph (80.5 km/hr)

A 1 U9.T (80.0) 73.

U

73.5

2 51.0 (o2.1j 73.5 73.2

B 1 51.3 (82.6) 72.6 72.2

2 51.0 io2.1j 73.2 72.9

C 1 51.3 (82.6) 71.0 70.6

2 52.4 (o4.3) 71.8 71.0

D 1 50.7 (81.6) 85.8 85.6

2 52.0 (83. T) 85.8 85.1

E 1 52.2 (8I4.O) 8U.0 83.3

2 50.9 (81.9) 83.8 83.5

E* 1 52. U (81+. 3) 82.8 82.0

2 51.9 (83.5) 8U.I4 83.8

Rl 1 50.9 (81.9) 75.0 7^.7

p sn n f 8n 76.0 76.0

Rl,2 1 50.0 (80.5) 77.2 77.2

2 ^9.5 (79. T) 78.1+ 78.6

R3 1 49.1 (79.0) 72. li 72.7

2 50. U (81.1) 72.8 72.7

28
Tatle 7. Maximum A-weighted sound levels, as measured at 50 feet Cl5-2 m), for

the h X 2 straight test vehicle operated in the coast and power passby

modes at a nominal speed of 55 mph (88.5 km/hr). These data are adjusted to 55 niph (88.5 km/hr) using a hO log V relationship between

sound level and vehicle speed and then are averaged for the two test

runs .

Test Test Actual Speed Maximum A--weighted Sound Level, dB re 20 yPa

Tire Run mph (km/hr) Adjusted Average

UOClC xu J J xupii V. OU. J Km/ nr ] 01 iwo xxuns

A 1 5U.3 (87.^) 75.0 75.2 75.2

(1. ( p . u 1 5 • -L

B 1 5U.8 (88.2) 7^.0 7^.1

v fRo 7k ft 7li ^

c

C 1 56.3 (90.6) 73.0 72.6 72.8

0

p Sf^ P f QD U

1

7 li 7 ^ n 1 0 . u A

S

D 1

err- /T I Qr\ ^:^ 55. D (,09. 5j 07 • D

A-v ), 07 . k At C 07 • D T

2 5U.I (87.1) 87.^ 87.7

E 1 55.8 (89.8) 8U.6 8U.3 8I1.6

2 56.1 (90.3) 85.2 8U.9

E* 1 56.3 (90.6) 86.0 85.6 85.5

2 56.1 (90.3) 85.6 85.3

A 1 57.1 (91.9) 80.6 79.9 79.^

S7 ? f QP P

1

7Q 78 0

B 1 56.3 (90.6) 80.2 79.8 79.8

d. ou . u (9.1

P C 1 56.3 (90.6) 80.

U

80.0 80.^

u

0d 55-4 loy.2j AnOU A. 0 An V OU . I W

E D 1 57.7 (92.9) 88.0 87.2 87.5

R 2 57.2 (92.1) 88.

U

87.7

E 1 57.0 (91.7) 87.

U

86.8 86.6

2 56.1 (90.3) 86.6 86.3

E* 1 55.7 (89.6) 86.6 86. li 86.

U

2 55.^ (89.2) 86.

U

86.3

29
Table 8. Maximxim A-veighted soimd levels, as measTored at 50 feet (15.2 m), for

the k X 2 tractor with single-axle trailer test -vehicle operated in the

coast and power passby modes at a nominal speed of 55 mph (88.5 km/hr).

These data are adjusted to 55 mph (.88.5 km/hr) using a hO log V relationship between sound level and vehicle speed and then are averaged

for the two test r\ans

.

Test Test Actual Speed Maximum A--weighted So\md Level, dB re 20 yPa

Tire

Code

Run

Number

mph (km/hr)

Measured

Adjusted

To 55 mph (88.5 km/hr)

Average

of Two Runs

A 1

2

5i+.3 (87.^)

5i+.5 (87.7)

79.6

79.6

79.8

79.8

79.8

c

B 1

2

53.0 (85.3)

5U.6 (87.9)

79.0

78.6

79.6

78.7

79.2

0

A

S

C 1

2

53.3 (85.8)

54. D (,07.9)

77.6

79 .0

78.1

79.1

78.6

T

D 1

2

52.2 (8I4.O)

53.5 (86.1)

86.6

87.8

87.5

88.3

87.9

E 1

2

53.3 (85.8)

55.5 (89.3)

85.0

86.

U

85.5

86.2

85.9

A 1

2

56.9 (91.6)

56.6 (91.1)

82.

U

82.2

81.8

81.7

81.8

P

B 1

2

57.5 (92.5)

56.3 (90.6)

83.^

82.8

82.6

82.

U

82.5

0

W

E

C 1

2

55.^ (89.2)

56.3 (90.6)

82.8

83.0

82.7

82.6

82.7

R

D 1

2

55.9 (90.0)

55.5 (89.3)

89.

U

89.

89.1

89.2

89.2

E 1

2

53.6 (86.3)

5U.1 (87.1)

87.2

88.0

87.6

88.3

88.0

30
TalDle 9. Maximum A-weighted sound levels, as measured at 50 feet Cl5-2 m), for

the \ X 2 tractor -with double-axle trailer test vehicle operated in

the coast and power passhy modes at a nominal speed of 55 mph (88.5

km/hr). These data are adjusted to 55 mph (88.5 km/hr) using a ho log V relationship between sound level and vehicle speed and then

are averaged for the two test rims.

Test Test Actual Speed Maximum A--weighted Sound Level, dB re 20 yPa

Tire Run nrnh (icTn/hr) A d i 1 ] <^ "h e d V C^^t^ Code Number Measured To 55 mph (88.5 km/hr) of Two Runs

A 1 s s s f 8q X) 78.6 78 h 7Q 0

2 55-^ (89.2) 79.6 79.5

"1 ss 1 (88 7) 78 8 78 8 78 S 2 56.0 (90.1) 78.5 78.2

c c 1 5U.8 (88.2) 77 k 77 S 78.0

0 2 56.7 (91.2) 79.0 78.5

A

S D 1 55.5 (89.3) 87.8 87.6 87.8

T 2 57.1 (91.9) 88.6 87.9

E 1 56.0 (90.1) 85.8 85.5 86.1

p >o.o \y ^ • ^ J 87 n 8f^

E* 1 56.0 (90.1) 87.0 86.7 86.

U

2 SS 1 (88 7) 86.0 86 0

A 1 56. U (90.8) 82.8 82 h 8? 0

2 56.3 (90.6) 82.0 81.6

B 1 5S 4 (89 2) 81.6 81 5 81 6

2 55.1 (88.7) 81.6 81.6

p c 1 56.1 (90.3) 82.2 81.9 81.8

0 2 55.5 (89.3) 81.8 81.6 w

E D 1 56.9 (91.6) 89.

U

88.8 88.5

R 2 56.0 (90.1) 88.5 88.2

E 1 55.1 (88.7) 86.6 86.6 86.8

2 5U.7 (88.0) 86.8 86.9

E* 1 55.1 (88.7) 87.^ 87.^ 87.3

2 5I1.I4 (87.5) 87.0 87.2

31
Table 10. Maximum A-veighted sound levels, as measured at 50 feet (15.2 m) , for

the U X 2 tractor vith double bottom trailer test vehicle operated in

the coast and pover passby modes at a nominal speed of 55 mph (88.5

km/hr). These data are adjusted to 55 mph (88.5 km/hr) using a

ho log V relationship between sound level and vehicle speed and then

are averaged for the two test runs.

^Test Test Actual Speed Maximum A--weighted Soiond Level, dB re 20 yPa

Tire mph (km/hr) Adjusted Average

Code Number Measured To 55 mph (88.5 km/hr") of Two Runs

A 1 5U.U (87.5) 8U.0 8U.2 8I4.O

2 55.5 (89.3) 8U.0 83.8

B 1 5,U.O (86.9) 82.8 83.1 83.6

c 2 5U.8 (88.2) 8I4.O 8U.1

0

C 1 55.0 (88.5) 83.8 83.8 83.9

A

s

oc.

'3 C ftV II 'I ' D V o ( . 4

;

0 :5 .

0

T

D 1 56.3 (90.6) 89.8 89. U 89.7

2 53.1 (85.5) 89.

u

90.0

E 1 55.9 (90.0) 88.2 87.9 87.8

2 53. T (86. U) 87.2 87.6

A 1 56.3 (90.6) 86.0 85.6 85.2

2 56.6 (91.1) 85.2 8U.7

B 1 56.1 (90.3) 85.8 85.5 85.2

P 2 56.5 (90.9) 85.

U

8U.9

0

¥ C 1 55. 7 (89.6) 85.0 8I1.8 8U.7

p ss 7 f Rq 6

)

8U.8 8U^-^ *-r • 6

R

D 1 55.6 (89.5) 90.0 89.8 90.0

2 55.8 (89.8) 90.

U

90.1

E 1 55.5 (89.3) 88.

U

88.2 88.6

2 57.5 (92.5) 89.8 89.0

32
Table 11. MaximTom A-weighted sound levels, as measured at 50 feet (l5.2 m) , for

the 6 X h straight test vehicle operated in the coast and pover passby

modes at a nominal speed of 55 mph (88.5 km/hr). These data are adjusted to 55 mpb (88.5 km/hr) using a hO log V relationship between

so\ind level and vehicle speed and then are averaged for the two test

ruas

.

Test Test Actual Speed Maximum A-weighted Sound Level, dE re 20 TiPa

XJ.X c Run mTiln ( Irm /"h y J Adjusted /\-\rpiy»Q rp(0

iT. V X cXgjC; Code Number Measured To 55 mph (88.5 km/hr) of Two Runs

A 1| f 8s Q 1 01 . U

Ai 81.6

2 53.3 (85.8) 81.2 81.7

]_ S6 f QO 6) 77.2 f D . 0 77 k

2 55.8 (89.8) 78.2 77.9

c c 1 56.7 (91.2) 1(O.d0 7 '-7 (5. 1 76 .0

0 2 55.8 (89.8) 76.6 76.3

A

S D 1 5U.8 (88.2) 90.2 90.3 90.6

T 2 5U.0 (86.9) n n n 9U. 9

E 1 5U.0 (86.9) 88.5 88.8 89.0

2 5U.5 (87.7) An n An 0 09.

E* 1 53.9 (86.7) 87.6 88.0 87.8

2 53.0 (85."^) 0 ( . U Ay

A 1 5=5 li (8q 2) 04 . u

A Q n 8? 6

2 5i+.8 (88.2) 83.2 83.3

"RU 1 Ao A 02 . 0 Ao )c 02 . 4

2 55.^ (89.2) 82.8 82.7

P r J- ? f Qn fi) An A Ol . 0

At li ol. 4

0 2 55.9 (90.0) 82.6 82.3

W

E D 1 56.5 (90.9) 91.^ 90.9 90.8

R 2 55.1 (88.7) 90.6 90.6

E 1 55.^ (89.2) 89.^ 89.3 89.3

2 55.7 (89.6) 89.

U

89.2

E* 1 5i+.3 (87. U) 89.2 89.

h

88.9

2 55. U (89.2) 88.

U

88.3

33
Table 12. MaximTom A-weighted sound levels, as measured at 50 feet (15.2 m) , for

the 6 x h tractor with double-axle trailer test vehicle operated in

the coast and power passhy modes at a nominal speed of 55 mph (88.5

km/hr) . These data are adjusted to 55 mph (88.5 km/hr) using a ho log V relationship between sound level and vehicle speed and then

are averaged for the two test runs.

Test Test Actual Speed Maximum A-weighted Sound Level, dB re 20 yPa

Tire Run mph \ km/hr ) Adjusted Average

Code Number Measured To 55 mph C88. 5 km/hr) of Two Runs

A 1 54.0 (00.2} Anou ft

. 0 An n 0(J . y 81 .1

2 55.9 (90.0) 81.6 81.3

B 1 56.0 (.91.^) o± . U AnoU )i . 4 80 .0

2 57.1 (91.9) 80.2 79.5

L C 1 54.0 (06.9) 78.

u

78.7 78.5

0 2 5U.0 (86.9) 78.0 78.3

A

S D 1 56.3 (90.6) 90.0 89.6 90.1

T 2 56.5 (90.9) y ± . u on

E 1 56.1 (90.3) 88.2 87.9 88.2

2 55.^ (89.2) 00 . D AP c:

E* 1 53.^ (85.9) 86.8 87.3 87.6

2 5^. 3 (87. U) 0 ( . D At a 0 ( . 0

A 1 56.3 (90.6) 03.0 83.3

2 56.6 (91.1) 83.6 83.1

B 1 56.0 (90.1) 03.

D

83.3 83.3

2 56.3 (90 6) 83.7 83.3

P C 1 56.7 (91.2) A Q n 82.6

0 2 56.2 (90. i+) 83.0 82.6 w

E D 1 56.1 (90.3) 91.8 91.5 90.7

R 2 56.1 (90.3) 91.2 89.9

E 1 5U.8 (88.2) 88.6 88.7 88.7

2 55.7 (89.6) 88.8 88.6

E* 1 5U.8 (88.2) 89. J+ 89.5 89.2

2 5U.T (88.0) 88.8 88.9

3h
The results of the model predictions of the maximinn A-weighted sound

levels are compared vith the measured values [average of the two test runs adjusted to 55 mph C88»5 km/hr) using a ^0 log V relationship between sound

level and vehicle speed] in Tables 13 and ik. For comparison purposes these

data are plotted as calculated versus measured values in Figiares ih and 15.

In general the agreement between the measured and predicted results is

quite encouraging — the average (absolute) difference being 0.86 dB for test

runs in the coast mode and 0.9^ dB for test runs in the power mode. As shown

by the dashed lines in Figure ik , a band of _+ 1.5 dB encompasses 88 percent of

the data points. In Figure 15 a similar band of +_ 1.5 dB encompasses t6

percent of the data points, and if the band is expanded to 2.0 dB this is

increased to 88 percent.

The largest discrepancy between the measured and calculated data occurs

for the 6 X h straight test vehicle equipped with tire A. In this case the

measured maximum A-weighted soiind levels appear to be too high. In the ideal

case of the combination of two identical incoherent sources (i.e., two axles)

an increase of 3 dB would be expected. Data published in the literature! i+] indicate that doubling the niimber of axles with loud tires increases the

maximum A-weighted sound level approximately 2 dB. A comparison of the k x 2

straight and 6 x h straight data show the following increases for the addition

of another axle:

tire A - 6.U dB

tire B - 3.0 dB

tire C - 3.2 dB

tire D - 3.0 dB

tire E - U.U dB

tire E* - 2.3 dB

These values all seem reasonable except for tires A and E. The k .k dB for

tire E is slightly high, but 6.h dB for tire A would appear to be incorrect

res-ulting from some undetected problem in data acquisition or analysis. The

original data tapes were rechecked but no obvious anomalies were discovered

for the 6 X h straight coastbys. One speculation concerns the possibility of

two different tread designs for tire A. As shown in Figure 6, the center rib

of tire A is diamond shaped, but in a previous study[9]j this identical brand

of tire had a zig-zag shaped center rib which has been shown to be

quieter [5 ,6] . Thus, if the h x 2 straight was equipped with a zig-zag shape

tread pattern and the 6 x h straight with a diamond shape tread pattern, the

increase in sound level would be greater than 3 to i| dB for the additional

axle as seen for the other test tires. This explanation cannot be verified

because the tires were borrowed to perform these tests and since then have

been returned.

A recheck of Tables 13 and ik shows that the larger variations between

the measured and calculated data occur primarily for tires D and E which are cross-bar type tires. These large discrepancies are believed to be due to

35
Tatle 13. Comparison of calcialated and measured maximum A-weighted

sound levels for test r\ins at 55 mph [88.5 km/hr) in the

coast mode

.

Test Maximum A-Weighted Sound Level, dB re 20 yPa

Test Tire Difference

Vehicle Code Measuredt Calculated (Calculated—Measured)

A 1 5 1 5 U

B V)i )i (4.5 0 .1

k X 2 STR c TO Q 72.0 72.2 —0. b

D 0 f . D At 0 07.2 — 0. 4

E 8U.6 85.1 0.5

E* 85.5 85.

U

-0.1

A 1 9 .9 U . 1

B T9 .2 79 .

3

0 •! k x 2 SAT c tA1 0 . D TD ~\ (9.1 0.

5

D

At n A^ T Ob . ( -1 .

2

E 85.9 85.3 -0.6

A TO n

(9 .U Tn(9 -D U . b

B tA c: (0 .

5

TO 1 (9.1 U . b

h X 2 DAT c 7A n 1 0 . U vA Q (0.9 u .9

D Ay0 a f • 0 Af^ 00 . Qy —n Q u. y

E 86.1 85.5 -0.6

E* 86.

U

85.8 -0.6

A All n A-:? A n 0

B A^0 ^ J . D A-3 0 A _j . 0 n 0

U X 2 DB c

A 0 n A 0 T 03 .7 —0.2

D

An T 89.7 A^ T OD . 7 —3.0.

E 87.8 85.5 -2.3

A

AtOl . D 77.9 -3.7

77-^ T^ Q 7d .0 —0. D

f.\J ^V h" RTRJ. 1\ c 76 .

0

75.1 -0.2

D 90 .6 89.3 -1.3

E 60 ,

0

At Q 07 . 0 —1.2

St. 8 87.1 ^0.7

A 81 .1 80.6 T^Q.5

B 80.

Q

79.7

6 X k DAT c 78.5 79.^ Q..9'

D 90.1 88.0 -2.1

E 88.2 86.7 -1.5

E* 87.6 86. U -1.2

t The measured values represent the average of data from

two test runs adjusted to 55 mph (88.5 km/hr) using a kO log V relationship between sound level and vehicle

speed (Tables 7 through 12).

36
Table ih. Comparison of calciilated and measured maximum A-weighted

sound levels for test runs at 55 mph (88.5 km/hr) in the

power mode.

Test M?^"yiTrmTn A — J. 1C3<.A Llil Lull -ti. Weighted Sound Level, dB re 20 yPa

X C O u TnJ. X TPJ. c; Difference

Vf^Vi "1 n 1 ^ 1*1 CX 0 U. ± \Z\X Calculated (Calculated-Measured)

A 81.1 1.7

B 79.8 80.9 1.1

li" -V- ^ p p.'vv, L— L_> -L 1\ c 80 U 80.6 0.2

T) 87 s 87.3 -0.2

X-j 8f^ 6 86.2 -O.H

86 U 85.7 -0. 7

A 81.8 82.4 0.6

B 82 5 8 2-. 2 -0.3

h X 2 SAT c 8? 7 81.9 -0.8

T) 8Q 2 87.4 -1.8

E 88.0 86.4 -1.6

A 82.0 82.3 0.3

B 81.6 82. 3 0.7

k X 2 DAT c 81.8 81.9 0.1

D 88.5 87.6 -0.9

E 86.8 86.

6

-0. 2

E* 87.

3

^ 1 • ^ 86.7 -0.6

A 85.2 84 .

9

-0.3

B 85 2 84.8 -0.4

I4. X 2 DB c 8U 7

Q 1, 0 04 . 8 0.1

D 90.0 87-3 -2.7

E 88.6 86.2 -2.4

A 8^.6 81.9 -1.7

B 82.6 81.

7

-0.9

6 X h STR c 81 9 81.

2

-0.7

D QD 8 89.7 -1.1

E 8q 88. 5 -0.8

E* 88.9 87.8 -1.1

A 83.3 82.7 -0.6

B 83.3 82.6 -0.7

6 X h DAT C 82.6 82.2 -O.ll

D 91.2 88.6 -2.6

E 88.7 87.5 -1.2

E* 89.2 87.2 -2.0

t The measured values represent the average of data from

two test runs adjusted to 55 mph (88.5 km/hr) using a

Uo log V relationship between sound level and vehicle

speed (Tables 7 throiogh 12).

37
70 75 80 85 90 95

MEASURED A-WEIGHTED SOUND LEVEL, dB re 20// Pa

Figure ih . Comparison of the calculated and measured maximum A-veighted sound

levels for runs at 55 mph (88.5 km/hr) in the coast mode.

38
MEASURED A-WEIGHTED SOUND LEVEL, dB ra 20 /< Pa

Figxire 15. Comparison of calculated and measured maximum A-veighted sound

levels for runs at 55 mph (88.5 kmAii") in the pover mode.

39
the load corrections applied to the input data. As pointed out in footnote

6 and discussed in more detail in Appendix A, at the time of this study only

a limited amount of data existed showing the influence of load on the

generated sounds levels. During a recent field test program conducted at

the U. S. Army Yuma Proving Ground, Yuma, Arizona in March 1976, additional

data on the influence of load on the generated so\md levels were obtained.

Data were measured for coastbys at 50 mph (80.5 km/hr) of a U x 2

single-chassis vehicle equipped with 11.00-2U.5 cross-bar tires (new tire D)

mounted on the drive axle and blank tires (full tread depth but no tread

pattern) on the steering axle. Measurements were taken for vehicle loadings

of 23 (corresponding to empty vehicle weight), 50, 60, 70, 80, 90 and 100

percent of maximtim rated tire load at 75 psi (5-2 x: 10 Pa) as recommended

by the Tire and Rim Association. These results (solid curve) and the

corresponding data used to apply the load corrections in the model

validation study (dashed curve) are shown in Figiore l6. As seen from this

plot, the relationship between load and generated sound level varies

significantly from the linear dependency assixmed in this study. For

example, if the certification tests were performed with a tire loading of

100 percent, but the in-service operating conditions were 70 percent, the

load corrections would be 3.9 "IB using the dashed cwrve (linear

relationship) and 0.9 based on the solid curve. This variation explains

why the model underestimates the maximiom A-weighted soTond levels for

cross-bar tires. Referring to Figures ih and 15, the roll-off at large

souad levels (i.e., data points corresponding to cross-bar tires) is due to

the assumed load corrections and is not a trend of the model to mderpredict

high noise levels.

Re-examining the results of the model computations treating rib and

cross-bar tires separately, the percentage of data points falling within

bands of +_ 1.5 and +_ 2.0 dB on Figures ih (coastbys) and 15 (powered

passbys) are given in Table 15. As shown by these values, the model more

accurately predicts the maximum A-weighted sound level for rib tires thaji

cross-bar tires. In fact if the 6 x U straight equipped with tire A is

disregarded, for coastby operations 100 percent of the data points fall

within a band of 1.0 dB. The accuracy of prediction for the powered

passbys is less, but considering the simple point soiorce model used to

represent the engine noise source the results are quite good.

Based on these results, it can be concluded that the model as presently

postulated gives a reliable estimate of the maximum A-weighted sound level

generated by a variety of vehicle and tire combinations. Before further

refinements can be made on the model more information on the effect of load

on the generated sound levels is needed.

ko
J5 1 1

MODEL VALIDATION STUDY

MARCH 1976 DATA

51.

75

yy

y

yy

y

yy

y

y

70

X

<

65 1 I

10 20 30 40 50 60 70

PERCENT OF MAXIMUM RATED TiRE LOAD

80 90 100

Figure l6. Comparison of load data obtained during a March 19T6 field test

program with the linear relationship used in the model validation

study. These data are for coast"bys of a 1| x 2 single-chassis vehicle

with cross-bar tires mounted on the drive axle operated at 50 mph

(80.5 km/hr) over an asphalt surface.

1+1
Table 15. Statistical comparison of the accuracy of the predictive model for rib and cross-bar tires.

Test Vehicle

Operational

Mode

Tire

lype

Percentage of data points falling

vithin the specified bands

+ 1.5 dB + 2.0 dB

Coast Rib 9^ 9^

Cross-Bar 81 81

Power Rib 89 100

Cross-Bar 63 81

5. Application of Predictive Model

One practical application of the DOT/NBS empirical truck tire noise predictive model is the estimation of the range of noise levels generated bytires with different certification levels mounted on various single-chassis

vehicles and tractor-trailer combinations[lO] . This information is useful in

determining what combination of tires can be used on a vehicle such that the

generated noise level meets the appropriate regiilatory limit.

To illustrate this application a series of tire noise certification

levels were selected which are representative of a broad cross-section of

tires on the road today. These certification levels are: T8 and 80 dB —

characteristic of rib truck tires, 82 dB — characteristic of noisy rib and

quiet cross-bar truck tires, 8U and 86 dB -- characteristic of cross-bar truck

tires, and 90 and 95 <3B — characteristic of pocket tread truck tires— [lO].

The necessary A-weighted sound level versus time data to be used as input to

the predictive model were chosen from actual passby time histories obtained in

the DOT/KBS truck tire noise study at Wallops Island, Virginia! 5 ,6 ] . The data

were chosen such that the maximum A-weighted so\and levels of the passby time

histories corresponded approximately to the T8, 80, 82, 8U, 86, 90 and 95 dB

certification levels. Prior to performing the calculations, the A—weighted

sound level time histories were uniformly adjusted such that the maximum

A-weighted sound levels were exactly T8 dB, 80 dB, etc. — These tires are included only for illustrative purposes and represent an upper limit of the sound levels generated by truck tires. The pocket

tread tire is no longer in use on the highway today because it does not con- form to the requirements of the U. S. Environmental Protection Agency

Motor Carrier Noise Emission Standard Uo CFR 202.23 which states that:

"No motor vehicle should be operated on any tire having a tread pattern com- posed primarily of cavities in the tread (excluding sipes and local chimking or irregularities of wear) which are not vented by grooves to the tire

shoulder or circiuaferentially to each other aro-und the tire"

.

U2
For this example seven different single-chassis and tractor-trailer

conibinations were examined. These vehicles are the same as described in the

previous section with the addition of a U x 2 triple bottom {h x 2 TB) which

is a U X 2 double bottom with another dolly and single-axle trailer attached

to the second trailer. Typical lineal dimensions of these vehicles are given

in Table l6 and the assumed axle loadings in Table IT- These loads are based

on a maximum legal limit permitted by the Federal-Aid Highway Act of 197^ [See

footnote 10] of 20,000 pounds (9,072 kg) on a single axle, 3^,000 poimds

(15,U22 kg) on tandem axles and 80,000 pounds (36,288 kg) total gross

combination weight for all vehicles except the ^ x 2 triple bottom which is

permitted a total gross combination weight of 105,000 poionds (U7,628 kg). It

is assumed that the tires for which the certification noise level applies are mounted on the drive axle(s), that rib tires whose characteristic noise level

is known to be low are mounted on the steering axle, and that half-worn rib

tires are mounted on all trailer axles. The engine is approximated by an omnidirectional point source located on the centerline of the vehicle directly

over the steering axle. For this example the A-weighted sound pressure level

of the engine is assiomed to be 83 dB at 50 feet (15.2 m) . This level

corresponds to the EPA standard for medium and heavy duty trucks which goes

into effect January 1, 1978.

The predicted in-service total truck noise levels at 50 feet Cl5.2 m) and

55 nrph (88.5 km/hr) are listed in the truck tire noise criteria chart shown in

Table l8. As an example of the use of this table, a U x 2 tractor with

double-axle trailer should be equipped with tires on the drive axle whose

certification level is Qh dB or less in order to meet the 90 dB total vehicle

noise limit of the Federal Interstate Motor Carrier Regulations for high speed

operations

.

Special caution should be taken in using this table for several reasons.

First, the sound level generated by truck tires is dependent on the state of

tread wear and in general increases with wear, in certain cases as much as ^+-5 dB[556]. Ideally, the maximum noise as a function of tread wear measured

according to the certification test procedures should be known if such a table

is to be used to estimate the maximiom in-service noise levels. If this

information is not available, the in-service noise levels predicted using the

certification levels for new tires must be adjusted to account for the

observed increases in tire noise as the tire wears in order to adequately

estimate the maximum in-service noise levels.

Another important point is that the values given in Table l8 are dependent upon the engine noise level. For example, if the engine noise level

was greater than 83 dB, the in-service noise levels woixLd increase and as a result the allowable tire certification level which would meet the regulatory

limit would decrease.

A final point to note is that in typical fleet operations, cross-bar type

tires run on the tractor drive axle(s) are removed after a certain state of

tread wear and mounted on the trailer to be worn down until they are ready to

be recapped. This can significantly increase the in-service noise level and

further reduce the allowable certification noise level for the drive axle(s)

tires

.

h3
Table l6. Ass-umed lineal dimensions in inches (meters) of

the seven vehicle configurations examined in

the example application of the predictive model.

The dimensions a through g are defined in the sketches

belov the table.

Vehicle Vehicle Dimensions, inches (m) a b c d e f g

h X 2 STR 1^5

(3.7)

h X 2 SAT 115

(2.9)

2ho

(6.1)

h X 2 DAT 115

V ^ • y / 351

^ 0 . y

;

52

V -L • 3 ^

i+ X 2 DB 115

(2.9)

2il0

(6.1)

73

(1.9)

2l|2

(6.1)

U X 2 TB 115

(2.9)

2I+O

(6.1)

73

(1.9)

2^2

(6.1)

73

(1.9)

2U2

(6.1)

6 X U STR 1^5

(3.7) (1.2)

6 X U DAT 115

(2.9)

52

(1.3)

325

(8.3)

52

(1.3)

ro o o o o o o

a —c e

o 00 o o

c
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C (D O (L) [> •H <U 0) -P +3 H

03 to O (U •H (U CO

"Vh ^ -H

•H -p

O

0)

O (U

o3

?H ft

(U S

-P•H^ UA O

CO o3 •Ho^ • •H UA

-P

H

Mq 4^ o

CO 0) (U

+:> -H 0) ^ CU O ^ ^

•H -H EH Uo

+3 • (U CO •H 0)

o3

EH

oo

EH

CO

•H CO 0) -P —- H

0) -H

<U

H 03 Eh o3 -P

U6
6. Appendix A

Model Computational Procedures

This appendix contains a general discussion of the "basic concepts

underlying the DOT/KBS empirical truck tire noise predictive model. To

illustrate these "basic concepts and the application of the model, an example

computation is presented.

6.1. General Assumptions of the Model

As previously stated in the Introduction, the "basic hypotheses of the

predictive model are: (a) that for any given single-chassis truck or tractor-trailer, each axle (actually the two or four tires mounted on the

axle) can "be treated as a single independent sound source, unaffected "by other

axles of the vehicle; and (h) that with a knowledge of the noise

characteristics of each axle for any particular set of operating conditions,

the in-service tire noise level for vehicles with numerous axles and axle

locations can "be estimated "by com"bining the contri"butions from each axle on an energy "basis

.

In the empirical model the axles (tires) of the vehicle are represented

as an array of sources spatially located according to the geometric

arrangement of the axles of the particular vehicle of interest. A primary

assumption of the model is that the sound generation characteristics of each

axle can "be represented "by tire noise certification data (A-weighted sound

level versus time data) if the number of tires mounted on the axle, the tread

design, and the state of tread wear of the tires are compara"ble.

A second assumption is that the certification data representative of each

axle can be adjusted to account for speed and load variations between the

certification test and in-service operating conditions. The tire noise

certification^data are measured according to prescribed procediores recommended

in SAE J5T[T]— . This standard specifies that the data be measured for

coastbys at 50 mph (80.5 km/hr) of a ^ x 2 single-chassis vehicle equipped

with "qiiiet" rib tires on the steering axle and the tires to be certified on the drive axle. The vehicle is operated in the loaded condition with tire

loading defined by the size and inflation pressure as recommended by the Tire

and Rim Association. To adjust the certification data to the in—service

operating conditions, speed and load corrections are applied.

Based on the data presented in the literature, it is assumed that the

generated tire noise levels increase with the fourth power of vehicle speed.

This relationship, given in terms of the change of A—weighted sound level,

AL , due to a variation in vehicle speed, V expressed in mph, from the

rererence speed of 55 niph (88.5 km/hr), is — In this current study data were obtained utilizing "fast" meter response

while SAE J5T specifies use of "slow" meter response.

hi
AL^ = kO log ^ (1)

This correction is uniforinly applied to the certification data for all types

of tire constructions and tread designs.

Only a limited amount of data investigating the effect of load on the

generated tire noise levels is available in the literature. These data exist

for only one type of rih and cross-bar tire, three states of tread wear —

new, half-worn and fully worn — and for only two loading conditions —

loaded, 17,720 pounds per axle (8038 kg per axle); and unloaded, 6l20 pounds

per axle (2776 kg per axle) [5,6]. In this current study it is assiomed that

the noise level changes linearly with load and that any rib or cross-bar tire

behaves with load changes exactly like the typical rib and cross-bar tires -for

which data exist. The corrections for variations in tire loading between the

certification test and in-service conditions are given in Figiire A-1. These

corrections, given in terms of load difference (certification loading minus

in-service loading) for new, half-worn and fiolly worn rib and cross-bar tires,

are uniformly applied to the certification data according to tread design and

state of tread wear.

To account for engine noise when predicting total in-service truck noise,

the engine was approximated by an omnidirectional point source located on the

centerline of the vehicle directly over the steering axle. The A-weighted

sound level [at 50 feet (15-2 m) from the centerline of travel] versus distance data for the passby of a point source is presented in Figure A-2.

For this study a level of 80 dB at 50 feet (15.2 m) was selected because of

good agreement with the measured data, but this curve can be used for any

engine noise level by vertically shifting the curve to the appropriate value.

These data are combined with the certification data to estimate the total

in-service truck noise.

Using these basic concepts and ass\jmptions , the computational procediare

for predicting the in-service noise levels is:

(a) Obtain the A-weighted sound level versus time certification data for

each axle of the vehicle of interest.

(b) Convert these data to A-weighted sound level versus distance data.

(c) Determine the speed and load corrections from Eq.uation 1 and Figiore

A-1, respectively, for each axle.

(d) Uniformly apply these corrections to the certification data and

replot the speed/load adjusted A-weighted sound level versus distance data for each axle.

(e) Combine the adjusted A-weighted sound level versus distance data for

each axle (also the engine if predicting total in-service truck

noise) after shifting the data by an appropriate distance

corresponding to the spatial separation of the axleCs) (or engine)

relative to a reference point such as the centerline of the front

drive axle

.
Figure A-1. A-weighted sound level corrections for variations in loading between

the certification test and in-service operating conditions. Load

difference = [certification loading — in-service loading]. Data

"were obtained from coastbys at 50 mpb C8O.5 km/hr) over an asphalt

surface with loadings of 17,720 and 6l20 pounds per a-xle (3038

and 2776 kg per axlel[5,61.

kg
-60

90

-40 -20

DISTANCE, meters

0 20 40

T CD aCM

C9

LU

<: 50

80 -

70

60

' ' «

« J_i '

I ' 'I L J LJ 'I I I I I

-200 -150 -100 -50 0 50

DISTANCE, feet

100 150 200

Figure A-2. A-veighted soxmd level [at 50 feet (l5-? m) from the centerline of

travel] versus distance for the passby of an omnidirectional point

source with an A-weighted sound level of 80 dB at 50 feet (15.2 m)

.

(f) Logarithmically add the A-veighted sound levels for all axles (and

the engine if predicting total in-service truck noise) at various

points along the passby to obtain the predicted A-weighted sound

level versus distance data (also the Tnaximum A-weighted sound level)

for the in-service operation of this vehicle.

These steps are illustrated in the following example.

6.2. Example Computation Using the Model

As an example of the application of the predictive model, the in-service

noise levels for the 6 x k tractor with double-axle trailer used in the model

validation study are predicted. The tractor is eqiiipped with rib tires whose

characteristic noise level is known to be low on the steering axle (the tire

noise contribution from the steering axle is neglected) and tire E —

half-worn bias ply cross-bar tires — on the drive axles. The double-aocle

trailer is equipped with tire R3 -- half-worn bias ply rib tires — on both

axles. The in-service noise levels are predicted for both coastbys and

powered passbys at 55 mph (88.5 km/hr) with the vehicle loading given in Table

3. The computational steps are performed as shown below.

50
a. Tire noise certification data

For the piirposes of this example, the certification test data vere

plotted by replaying the original data tapes through a graphic level recorder.

These A-weighted sound level ver^gs time data are given in Figures A-3 and A-^

for tires E and R3, respectively— .

h. Convert time data to distance data

The time data are converted to distance data by using the points on the

time history plot corresponding to the start and end of the test section, or

as an alternative, the point corresponding to the start of the test section

and the average vehicle speed through the test section. In either case, the

distance conversion is an approximation because the speed is decreasing as the

vehicle coasts through the test section. In this example, the start point and

average vehicle speed are used to convert to distance using the simple

relationship,

X = 1.1+7 Vt , (2)

where x = distance, feet

V = vehicle speed, mph

t = time, seconds.

The A-weighted sound level versus distance data for tires E and R3 are given

in Figures A-5 and A-6, respectively. These curves have been replotted

limiting the abscissa to j+200 feet (_+ 6l m) using a sign convention of plus

for positions before the drive axle reaches the microphone and minus for

positions after it passes. The zero point — point corresponding to the

passage of the drive axle of the 1| x 2 single-chassis vehicle by the

microphone — is located 309.8 feet i9'^.h m) from the point corresponding to

the start of the test section. This distance is equal to one-half the length

of the test section [300 feet {91-^ m)] plus the distance between the steering

and drive axle of the U x 2 single-chassis vehicle [9.8 feet (.3.0 m) ] which is

necessary because the data start signal recorded on tape is activated by the

steering axle

.

c. Speed and load corrections

The vehicle speeds for the two certification test runs are 50.9 mph C81.9

km/hr) for tire E and 50.1+ mph (8I.I km/hr) for tire R3. Using Equation 1,

the speed corrections are calculated to be l.h dB for tire E and 1.5 dB for

tire R3.

— Because of the transient response characteristics of a graphic level

recorder, the maximum A-weighted sound levels shown in Figures A—3 and A—

U

are less than the values reported in Table 6 which were obtained using a real time analyzer as shown in Figure 13.

51
S 90

^01234567

< TIME, seconds

Figiire A-3. A-veighted sound level versus time certification data for tire E. Vehicle speed is 50.9 mph (8l.9 km/hr) and loading is l8,080 pounds

per axle (8201 kg per axle).

I <

3 4

TIME, seconds

Figure A-^. A-weighted sound level versus time certification data for tire R3.

Vehicle speed is 50.1+ mph (8l.l km/hr) and loading is l8,080 pounds

per axle (8201 kg per axle).

52
ca 0.oesi o

do

-60 -40 -20 DISTANCE, meters

0 20 40 60

oa 80

Q 70 -

a

LU 60

C9

Ui

I <

50 J—l I I I I I I L I J I I I I I I I I 1 I I I I I I I

I I I I ''

-200 -150 -100 -50 0 50

DISTANCE, feet

100 150 200

Figure A-5 . A-weighted soijnd. level versus distance certification data for tire

E. The zero point corresponds to the passage of the drive axle of

the U X 2 single-chassis vehicle "by the microphone.

-60

21

111

90

80

70

1= 60

3

<

50

-40 DISTANCE, meters-20 0 20

T

J I I l__L_l I L_l I 1_1 I I I I l_l L I

1

I

40 60

' I I ... I -200 -150 -100 -50 0 50

DISTANCE, feet

100 150 200

Fig\are A-6. A-weighted sound level versus distance certification data for tire

R3. The zero point corresponds to the passage of the drive axle of

the h X 2 single-chassis vehicle "by the microphone.

53
The loading for the 6 x h tractor with douhle-axle trailer is given in

Table 3. Since the axle loadings are different, a separate load correction is

calculated for each axle. The axle loadings, load difference [certification

loading of l8,080 pounds per axle (8201 kg per axle) minus the in-service load

per axle] and load corrections determined from Figiire A-1 are summarized in

Table A-1. Also presented in Table A-1 are the total corrections [combination

of speed and load corrections] vhich are applied to the tire noise

certification data for each axle.

d. Adjusted A-weighted sound level versus distance certification data

The speed and load corrections are uniformly applied to the certification

data for each axle by shifting the entire A-weighted sound level versus distance curve vertically up or dovn by an amount corresponding to the total

correction. The adjusted certification data for each axle are then replotted

using the same scale for distance on the abscissa of each plot so that the

data can be easily combined as described in the next step. These four plots

are not shown here because the distance scales — determined by vehicle speed — are approximately the same for tire E and tire R3 certification data as shown in Figures A-5 and A-6.

e. Combination of certification data for all axles

The certification data for the four axles are combined by plotting the

A-weighted sound level versus distance data on the same graph with the

appropriate shifts to account for the spatial separations of the axles. Using

the front drive axle centerline as the reference or zero point, the shifts for

the other axles are: -k.2 feet (-1.3 m) for the rear drive axle; -33.0 feet

(-10.1 m) for the front axle of the trailer; and -37-3 feet (-11.1+ m) for the

rear axle of the trailer. For the powered passby case, the engine shift is

+12 feet (+3..T m) • The combinations of the adjusted certification data using

the appropriate shifts are shown in Figiores A-7 and A-8 for the coastby and

powered passby cases, respectively.

f . Predicted A-weighted sound levels

The predicted A-weighted soimd levels are determined by combining the

A-weighted levels for each of the four axles (_ and the engine for powered

passbys) at various points along the passby. For example, in Figure A-7 the

levels at +50 feet (15-2 m) are 8U.0 and 82.7 dB for the drive axles and 72.

U

and 71.6 dB for the trailer axles. These levels combine to give a predicted

A-weighted sound level of 86.7 dB. The predicted A-weighted sound level

versus distance data are plotted in Figures A-7 and A-8.

The data measured for an actual passby of the 6 x h tractor with

double-axle trailer were also plotted using a graphic level recorder. These

data [adjusted to 55 niph (88.5 km/hr) using Equation l] are compared with the

predicted A-weighted soimd levels in Figure A-9. These predicted levels agree

well with the measured data especially considering the graphical technique

used.

3h
03 0 O

-P •H + o on LTN VD ^ -P CM O o o H H

H •H <u <U 03 <D 1 + + +

03 0) 0) O ^

+3 > ft O 1 O cn m

Eh < O ^ oJ ^ CM ^ a

o

-P •H

-P • • • • M O H H H

•H 0) + + + +

(U 0)

Is

1

<Dft

!hO

oo O CO g < ra o -p -

EHo

•H

-p

03O C7\ On

•H <u «H H O H O H O H CD H •H O ir\ CO OO Lf\ OO LTN CO

-P p •H (U \ ^—

^—

—

-

w ^

(D 0 ft ft >i O Eh > cn fi ^

o3

•> Ph

t3 G 3-

<U o

-P •H o t- CM H

P CM O H o O O •H (U (U 1 1 + +

cu

o3 ^ 9 ° 9 < 1-^ O

,—

.

O OJ o -J- o vo O D—

OO ON CO H CvJ CM

(1) t:} t— CM LTN VD VD CVI on

CM rH CM rH ^

o3 —

O •H O ^

Q ft

m '—

'—

o o\ O O LTN o j0) q — ir\ o O CO VD t—

o3 P bO t^N CO CO o o VD >- LTWD J ft

H — H —

H

u cn on

•iH K E-t

<D ^

r—1 d) X H

o <; -H

•H o3 < o3 +3 -P (U 0) -p ^

•H > <u ^ >> 0 S EH 5h eh

caO

O -H r-| ^ X

03 -H rH

(D ^ X o 03<U Ch < P-> Q < K O < FiH O cr; o

55
-60 -40 -20

DISTANCE, meters

0 20 40

100

CO a.

CVJ w

CQ

>

LU

_l

O

90

80

ooo 70

a

X

60

50

60

1 1 1 1 1 1 1 1 1 1 1 1

I Jn

II i| PREDICTED

l| |i LEVELS

^^^^^^^^TRA^^^^\^

"^^^^^^^

DRIVE / X

^=5^ AXLES

1 1 1 1 1 r 1 1 1 1 1 1 1 1 1 1 1 1 1

TRAILER ^.^^^^

AXLES

1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1

-200 -150 -100 -50 0 50

DISTANCE, feet

100 150 200

Figure A-T- Predicted A-weighted sound level versus distance data at 50 feet

(15.2 m) for the passby of the 6 x U tractor with double-axle

trailer at 55 mph (88.5 km/hr) in the coast mode.

56
Figure A-8. Predicted A-weighted sound level versus distance data at 50 feet

(15.2 m) for the passby of the 6 x h tractor with double-axle

trailer at 55 mph (88.5 km/hr) in the power mode.

57
Figure A-9. Comparison of predicted and measured A-weighted souind level versus distance data at 50 feet (15-2 m) for the passby of the 6 x k

tractor vith double-axle trailer at 55 mph (88.5 km/hr) in the

coast mode. Measured data were corrected to 55 mph (88.5 km/hr)

using Equation 1.

58
T. Appendix B. SAE Standard for Measurement of Truck Tire Noise^

SOUND LEVEL OF HIGHVMY

TRUCK TIRES—SAE J57 SAE Recommended Practice

Report of Vehicle Sound U^el Coimnillee approved Jul) IV. i

1. Introduction—This SAE Recommended Practice establishes a test procedure for measuring the sound level produced by tires intended

primarily for highway use 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 50 mph (80 km/h) 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 basis of reported levels. Reference to sound levels is given in the Appendix.

2. Instrumentation—The following instrumentation shall be used

for the measurements as required:

2.1 A sound le\'el meter which satisfies the Type I requirements of ANSI SI.4-1971. Specification for Sound Level Meters.

2.1.1 .\s 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 indicating meter. pro\iding the system meets the requirements of S.\E J18-1. with

"slow" response specified in place of "fast" as applicable in paragraph

3.6 therein.

2.2 An acoustical calibrator for establishing the calibration of the sound level meter and associated instrumentation.

2.3 .An anemometer.

J. Test Site

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 100 ft (30 m) of the measurement area.

3.2 The vehicle path shall be relatively smooth, semipolished. dry, Portland concrete which is free of extraneous surface material.

3.3 The microphone shall be located 50 ft (13 m) from the centerline of the vehicle path at a height of 4 ft (1.2 m) above the ground

plane. The normal to the \ehicle path from the microphone shall establish the microphone point on the vehicle path. See Fig. 1. 3.4 The test zone extends 50 ft (15 m) on either side of the micro- phone point along the \ehiclc 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 material and. in any event, shall be free of powdery snow, grass, loose 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 12 mph (19 km/h).

4. Test Vehicle

4.1 The vehicle shall be a motor truck equipped with two axles (a nonpowcred steering axle and a powered axle).

4.2 The vehicle shall ha\*e a platform, rack, or van body capable

of retaining the loading or ballast. This body shall have an essentially

flat and horizontal undersurfacc. and be moimtcd such that this surface has a 5 ±1 in (127 ±25 mm) minimum clearance vvith the tire fully loaded. This body shall be nominally 96 in (2440 mm) in width and

extend a minimum of 36 in (910 mm) rearward of the rear (povvered) axle centerline.

4.3 Mud flaps should be remo\'cd 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 be mounted singly. A tire used as both duals and

singles may require test at both dual and single mounting. The sound

level reported must be identified as to t)pe of mounting.

5.2 The tires shall be inflated to the maximum pressure and

loaded to the maximum load specified by the Tire and Rim Associa- tion for continuous operation at highway speeds exceeding 50 mph

(80 km/h).

5.2.1 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 pres- sure, provided the load is not less than 15% of the maximum rated

load.

.As an alternative, the pressure in the tires can be adjusted to cor- respond to the actual load following the appropriate load/pressure

tables in the Tire and Rim Association Yearbook. Because the choice of procedure may cause small differences in level, such levels may not be reported as absolute 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 (such as coasting) that the sound level due to the engine and other mechanical

NOTE DIMENSIONS ARE FT [ir FIG. 1-TEST Sn E (SEE PARAGRAPH 3). (VEHICLE MAY BE RL.V IN EITHER DIRECTION)

—7/Reprinted with permission, "Copyright © Society of Automotive Engineer

Inc., 1975, All rights reserved."

59
sources is minimized Ihroughout the test zone. The vehicle speed at the microphone point shall l)e 50 mph (80 km/h).

6.2 T he sound level meter shall be set for "slow" response and the A wcighting network. The observer shall record the highest level at- tained 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 level recorder.

6.3 There shall be at least three measurements. The number of measurements shall equal or exceed the range in decibels of the levels obtained.

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

7. General Comments

7.1 It is recommended that technically competent personnel select the equipment lo be used for the 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 lo the prac

tices recommended in the operating manuals or other literature pro

vided by the manufacturer. All stated precautions should be observed Some specific items for consideration arc;

7.2.1 Specifications for orientation of the microphone relative to th( ground plane and the source of sound should be adhered to. (Assum<

that the sound source is located at the microphone point.)

7.2.2 Proper signal le\cls. terminating impedances, and cable length- should be maintained on all multi-instrument measurement systems.

7.2.3 The effect of extension cables and other components should be

taken into account in the calibration procedure.

7.2.4 The position of the observer relative to the microphone should

be as recommended.

7.3 Instrument manufacturer's recommended calibration procedure and schedule for individual instruments should be employed. Field calibrations should be made immediately before and after testing each

set of tires. 7.4 Not more than one person, other than the observer reading the

meter, shall be within 50 ft (15 m) of the vehicle path or the micro- phone, and that person shall be 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 equipped with quiet tires is at least 10 dB

below that of the vehicle equipped with test tires. The sound levels obtained with this procedure 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 310 dB lower than when equipped with the tires being tested.

S. Reference Material—Suggested reference material is as follows:

8.1 ANSI SI . 1 1960, Acoustical Terminolog)'

8.2 ANSI SI.2 1962, Physical Measurement of Sound

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

8.4 S.'VE J184, Qualifying a Sound Data Acquisition System

8.5 1 ire and Rim Association Yearbook

Applications for copies of the ANSI documents should be addressed

to the American National Standards Institute, Inc., 1430 Broadway, New

York, New York 10018. APPENDIX

Al. An A-weighted sound level exceeding 85 dB, determined in ac- cordance with this recommended practice, is not consistent with present

best current practice for cross ribbed tires in normal states of wear. It

is general experience that the sound level of unworn tires is significantly

less than that of worn tires. A2. Road surfaces are known to significantly affect the sound level exhibited by truck tires. The vehicle path surface specified herein is not sufficiently defined to eliminate variations in sound level due to surface (see paragraph 3.2). 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 arc factors that direct attention to the sound, and are important determinants of the accept

ability of the sound.

Insufficient data are available concerning the measurement of the sound from distant truck tires and the significance of these sounds compared to the sound levels measured with this procedure.

60
8. References

[l] Kibbee, L. C, The Noise Trucks Make - Report of Tests (American Trucking

Associations, Inc., Washington,, D. C, I96U).

[2] Anon. , Truck Tire Noise, Presentation ty the Rubber Manufacturers

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

Environmental Protection Agency, Washington, D. C, November 12, 19T1.

[3] Lippmann, S. A., Establishing a Testing Standard for Truck Tire Sounds,

published in SAE Report SP-3T3: Truck Tire Noise (Society of Automotive

Engineers, Inc., Warrendale, PA, 1972).

[h] Tetlo-w, D., Truck Tire Noise, S )V Sound and Vibration 5. (8), 17-23

(1971).

[5] Anon., Truck Noise-I, Peak A-Weighted Sound Levels Due to Truck Tires, U.

S. Department of Transportation Report OST-ONA-71-9 (National Bureau of

Standards, Washington, D. C, 1970).

[6] 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 OST/TST-72-1 (National

Bureau of Standards, Washington, D. C, 197^)-

[7] Society of Automotive Engineers, Inc., J^7 - Sound Level of Highvay Truck

Tires, SAE Recommended Practice (Society of Automotive Engineers, Inc.,

Warrendale, PA, 1973).

[8] American Society for Testing and Materials, D 22^0-75, Standard Method 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).

[9] 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 DOT-TST- 7^-21 (National Bureau of Standards,

Washington, D. C, 197^).

[10] Close, W. H., Should There Be Truck Tire Noise Regiilations? , S)V Sound

and Vibration 9 (2), 2U-27 (1975).

61
Acknowledgements

The authors would like to recognize the contributions made by the following organizations which have greatly aided this program: the staff of the U.

S. Army Yvaaa. Proving Ground especially Mr. Francis E. Northon and Mr-. Elmer

Hockman; Mr. L. L. Lehr of Firestone Tire and Rubber Company, Mr. J. D.

Eagleburger of Goodyear Tire and Rubber Company and Mr. G. H. Secrist of IML

Freight, Inc. for the loan of test tires; and Mr. M. Daggett of Ryder Truck

Rental, Inc. for the loan of test tires and assistance in locating appropriate

test vehicles.

The authors also express appreciation to Mr. R. L. Fisher for his

assistance in data reduction and analysis, to Mrs. J. R. Russell for the

typing and preparation of the manuscript.

62

I

I