Reference road surfaces for use in tire/road noise measurements

ISS/V 0347-5049

[i VTISärtryck

104 1.985

Reference Road Surfaces for Use in

Tire/Road Noise Measurements

Ulf Sandberg and Jerzy A. Ejsmont

Reprint from the 7985 International Conference on Noise Centro/

Engineering (INTER-N0/8E 85) in Munich, Federal Republic of

Germany, 78-20 September 7985

VTI, Linköping 7985

Vag-00h Tia k- Statens väg- och trafikinstitut (VTI) . 58 7 o 1 Linköping

ISSN 0347-6049

VTIsärtryck

_ii

104 1.985

Reference Road Surfaces for Use in

Tire/Raad Noise Measurements

Ulf Sandberg and Jerzy A. Ejsmont

Reprint from the 7985 International Conference on Noise Contro/

Engineering (INTER-N0/SE 85) in Munich, Federal Republic of

Germany, 78-20 September 7.985

VTI, Linköping 7985

Vag-00/1 Efi/(- Statens väg- och trafikinstitut (VTI) . 581 01 Linköping

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REFERENCE ROAD SURFACES FOR USE IN TIRE/ROAD NOISE MEASUREMENTS

Ulf Sandberg Jerzy A. Ejsmont

Swedish Road and Traffic Research Institute Technical University of Gdansk

5-581 01 Linköping

ULMajakowskiego 11/12

SWEDEN PL-80-952 Gdansk, POLAND

(presently at III. Physik. Inst.,

Univ. of Göttingen, BRD)

INTRODUCTION

Tire/road noise measurements have become very important during recent years due to the awareness of the problem of tire/road noise emission in free-flowing traffic. There is a demand for standardization in this field, especially as various methods have been in use and results have had a poor repeatability. One of the problems has been to control the road surface influence as no reference surfaces have been in use.

The Group of Rapporteurs on Brakes and Running Gear (GRRF) within the ECE has established an ad-hoc group on "Measurement of tire/road noise" which recently prOposed three methods for tire/road noise measurements (ref. l). These methods are: a conventional coast-by method, a trailer method and a laboratory drum method. The prOposal includes the Specification of two reference surfaces by measurement of their macrotexture. One is designed to excite maximum high frequency noise (smooth surface) and the other to excite maximum low frequency noise (rough surface). Macrotexture should be measured by profile registration and subsequent spectral analyses where the levels in two critical octave bands are required. When the surfaces do not correspond to the nominal texture values, a correction to the noise for deviating texture is applied.

The background for this problem and some information on which the prOposal is based are presented in this paper.

EXPERIMENTAL DESIGN

All measurements were actually made both by the coast by and the trailer methods, according to the prOposed standard, although here we concentrate only on the first method. During the measurements 8 different tires were used: tire "P" : PIARC ref. tire with smooth tread, "S" : Firestone Cavallino 8-1, "M" : Michelin XZX, "W" : Firestone M+S Town & Country, "G" : Gislaved M+S Frost, "GS" : Gislaved Frost with 108 studs, "WD" : Dun10p SP88 M+S, "SP" : Pirelli P3.

The test surfaces are presented in table 1. The last two digits in the number

are the year of measurement. Surfaces 1, 2 and 3 (artificial ones) are all located

on untrafficked test tracks, whereas the others were trafficked roads. Of these, No. 1 and 2 were constructed to simulate real road surfaces on the test track.

Fig. 1 shows the macrotexture values which are required for characterization according to the prOposed standard and the "ideal" values with tolerance

2

Sandberg

10 3 mm) within the octave band with center texture wavelength of 80 mm. L5 is

the correSponding for the texture wavelength 5 mm. It has been found earlier that such surface descriptors are relevant for characterization in this case (ref. 2). Table 1. Description of the road surfaces

No. Name Description

1-83 Nivecim Asphalt concrete MABlZT + sealed with Nivecim 1-84 Nivecim As 1-83, but also painted 3 times with Nivelan 2-83 Yl 8 12 Single surface dressing, chippings 8 12 mm

2 84 Yl 8-12 As 2 83, but coated by a thin bituminous + sand layer

3-83 MABlZT ASphalt concrete, chippings _<_12 mm 3-814 MABlZT As 3 83

4-83 MABlZT Very smooth and dense aSphalt concrete. chippings 512 mm

5 83 Yl 12-16 Single surface dressing, chippings 12-16 mm

6-84 Yl 12-16 Single surface dressing, chippings 12-16 mm

7-84 MABlZT Very smooth and dense aSphalt concrete, chippings 512 mm

60 as '; : 3 $ 8 % m... SPEEDS: "' '_' A- 30 kun/h *

%

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_{g 754-}

u so km/h

*

o- 70 k.../h

?

250 g * 90 km/h e * å E 70" %

:=;

> 65"

3

Sw- g i B :F 60- - h

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S's-v- A 30 Tgif- .. - so : + i 11 % 1'

30 40_{.-Fine macrotexture level L5 [dB]}50 ,. so so 55 so_{LA on ROUGH surface}as 70 75 _[dB(A)]so as Fig. 1. Macrotexture values of the sur- Fig. 2. Tire/road noise of the 7 non faces as required by the proposed stan studded tires on a smooth versus a dard. Squares show the tolerance window. rough surface.

THE NEED FOR TWO REFERENCE SURFACES

But why use tll/_o reference surfaces? Fig. 2 gives the answer: for each Speed the ranking of tires is completely different on a smooth compared to a rough surface. In fact, the partial correlation coefficient between noise levels on the smooth and rough surfaces in fig. 2 is -D.75. The reason is that these two surfaces are exciting each of (at least) two tire noise generating mechanisms in a very different way (ref. 2). The two prOposed reference surfaces have been chosen to distinguish prOperly between these two mechanisms. 50, using only one surface would give a very limited information. In practice, it is very common that smooth surfaces are used on low speed roads in urban/suburban areas and rough surfaces are used on high-Speed roads in suburban or rural areas.

REPEATABILITY OVER TIME

Of the surfaces used, No. 3 was unchanged between the years 1983 and 1984 and the results on this surface can illustrate the repeatability over time when the

3

Sandberg macrotexture is not changing. Fig. 3 shows the average spectra for six tires and

four speeds measured 1983 and 84. The deviation in the important range 200-5000

Hz is not higher than 1 dB, which is remarkably good.

Surface No. 3 is, by the way, a typical test track aSphalt surface. As may be seen by comparing fig. 3 and 5 it combines the low noise characteristics of each of the other surfaces and is thus not representative of road conditions.

80 80 [dB] _{sum-mce No 3} [dB_{] _} TIRES: P,S,M,W,G,GS SPEED. 70 km/h YEAR: - - 1983 70" - - - 1984 70- _o-60 70 km/h

A LA so 50 km/h _ dB(A) 50-- _T 30 knvh " ~ ~ 0.2 SURFACES- \ ~ 0.4 ₅₀_» _{No.4 (1983) Smooth, 73.9 dB64) \'\ \}" *

0.4 --- No.5 (1983) Rough, 76.0 dBW \\ 01 - --- N06 (1984) Smooth, 75.1 dB(A) så 1 . ' _ _ No.7 (1984) Rough, 75.9 dBM) 30 I I TL I l :j "I T I I I l l : l I A} l I If I l 40 | ' ll l I : l I lr # I J]: j T + ' ' % ' l % _l ' I 25 250 500 I K 2K 4K GK i 25 250 500 I K 2K 4K SK FREQUENCY [Hz]

Fig. 3. Tire/road noise for 8 tires

(average) measured on the same surface

FREQENCY [dB]

Fig. 4. Tire/road noise measured 1983 or 1984 on four road surfaces

two consecutive years. L values are which are similar pair by pair. A-weighted diff. between 1984 and 1983.

REPEATABILITY OVER TIME AND LOCATION

Surfaces 4-83 and 7-84 were chosen to be similar and within the tolerances of the smooth reference surface. Similarly, surfaces 5 83 and 6 84 were chosen as rough reference surfaces. Of course, they were not identical, see fig. 1, and they were measured in different years. Anyway, the results were quite repeatable as can be seen in fig. 4. The difference between 4-83 and 7 84 below 300 Hz can be explained by a macrotexture difference at long texture wavelengths, but the difference of ca 2 dB above 1 kHz is unexplained so far.

ROAD VERSUS ARTIFICIAL SURFACES

The reference surface qualities have been chosen so that the surfaces can easily be found on trafficked roads, but it is desirable that reference surfaces can also be constructed on test tracks and that they give results equivalent to results measured on roads. Fig. 5 shows a comparison of tire/road noise emission

(averaged for six tires) measured on trafficked roads (No. 4-83 and 5-83) as well

as on corresponding artificial surfaces on a test track (No. 1 83 and 2-83). In the low frequency range the results compare very well pair by pair, as is the case for the rough surfaces also at high frequencies. The problem is the medium and high-frequency range for the smooth surfaces, where the artificial surface obviously excites these frequencies too little. However, it should be noted that 2 dB of the 5 dB noise deviation can be explained by the texture difference (L5 in fig. 1) as a correction in noise of 50% of the level difference in texture is recommended in the pr0posed standard, but this is not enough to explain the whole difference. Results from measurements in 1984 (after sealing the surface by thin paint) confirm this conclusion.

It seems like the smooth untrafficked artificial surface does not perform as predicted from texture measurements. Measurements of friction coefficient made on these surfaces in dry condition, which is an indirect measurement of microtexture, indicated that the friction of the artificial surface is lower than the friction of the corresponding trafficked road (which was contrary to our

Sandberg

expectation). However, such friction influence, for similar macrotexture, has not

yet been verified by any other field experiment so it must still be considered as

very uncertain. In addition, between the years 1983 and 1984 surface 1 was painted three times to decrease its friction, but this had absolutely no effect on

noise, as seen in fig. 6. Whatever the reason, it is obvious that more work is required before a smooth surface on a test track can be suggested.

[dB] TIRES P,S,M,W,G,GS 1 SPEED 70 km/h 1983 70 601 \ 50-*- SURFACES TX TN.

No 1 Smooth artnfucnal 71.6 dB(A) \\ X ... No 2 Rough artlfscual, 75.5 dB(A) ____

No. 4 Smooth road, 73.9 dB(A)

__- No 5 Rough road, 76.1 dB(A)

4C I [L I I % I I % I I+ I I % I l : l I % I

i25 250 500 TK 2K 4K BK

FREQUENCY [H z]

Fig. 5. Tire/road noise on a pair of

road surfaces compared with a pair of artificial test track surfaces.

80 [dB] TIRES' P, S, M,W, G, GS_{SPEED 70 kmlh} 70 60

50 __ SURFACES No 1 (1983). 71.6dB(A) - N01 (1984). 72.3dB(A) 40 l A} I I I I % I I % I l | I I % I I i l 125 250 soo 1x 2x 4|< ax FREQUENCY [Hz]

Fig. 6. The effect on tire/road noise

of painting surface 1 83 three times

N01

with a "lacquer". CONCLUSIONS

se, texture and friction measurements made during two years on different surfaces qualified as reference surfaces for tire/road noise tests, according to a recent proposal, have shown the following:

0 Noise ranking of tires is very different depending on whether the surface is of

"rough" or "smooth" type. Therefore two reference surfaces must be used. The repeatability of noise Spectral measurements over one year for a non-changing surface macrotexture is excellent (provided the tires are not

changing their prOperties).

Reference surfaces selected on different locations on trafficked roads gave repeatable results.

The use of "medium-smooth" aSphalt, common on test tracks, is not recom mended in this case as it results in too low noise levels.

Trials to construct a rough reference surface on a non trafficked test track were successful - the result was the same as for correSponding road surfaces. Trials with a smooth (artificial) reference surface on the same test track failed. The noise levels at high frequencies were too low to represent road conditions. The reasons for this are still to be investigated.

REFERENCES

GRRF Ad hoc Group on methods for measurement of tyre/road noise: "Me thods for measurement of tyre/road noise First pr0posal for a provisional

methodology. Revised according to meeting 1985-03-21/22".

Sandberg, U., Descornet, G.: Road surface influence on tire/road noise Part I Descornet, G., Sandberg, U: Road surface influence on tire/road noise - Part II VTI preprint No. 56, Swedish Road and Traffic Research Institute, Linköping,

5

Sandberg

APPENDIX Enlarged figures

Sandberg Fi ... ...'.'..:.:..."".""""' . . _..'".... '..."""""""""""""....""" ' . ...'...."'"... .' ."."....'.. ...____'...'...""""' '.. .. . ...'_____... """'..."""""". '. Co ur se ma cr ot ex tu re leve l" L8 0 [d B] ... ... ""'.."" ...""'..."""""". ...___...""...""" '. .. ". . .... .._ _... .'.... ... . ' ...'..""'... ___-..._.____... . H..."... '.. ....

Fine macrotexture level

Macrotexture values of the surfaces as r standard. Squares show the tolerance windows

Ls [dB]

[d B( )]

%

I l I l l

3

8

l | LA on S M O O T H su rf ac e ) ] L 1 I I I r I 60 75 80 LA on ROUGH surface B ed by the proposed

Tire/road noise of the 7 non-studded tires on a smooth versus a rough

7 Sandberg SURFACE No 3 YEAR 3 1983

- - 1984

30 l I 11 l l % j | % 1 l % l 1 lr r l % I l % j ' 125 250 500 1K 2K 4K BK

FREQUENCY [Hz]

Fig. 3 Tire/road noise for 8 tires (average) measured on the same surface two

consecutive years. AL values are A-weighted difference between 1984 and 1983

80

TIRES: P,S,M,W,G,GS

[dB] _

SPEED: 70 km/h

70-SURFACES. sx *.. \

No.4 (1983) Smooth, 73.9 dB(A) \'\\

_____ No.5 (1983) Rough, 76.0 dBM)

NN

J

No.6 (1984) Smooth, 75-7 dB(A)

&_.

_\

__ _ No.7 (1984) Rough,

75.9 dB(A)

40 _{T I} 1_{I l I} l_{I l 7 r}| _{T | r}| _{j I I}| _{__] l} |_{| I} |_{l l l}

125 250 500 1K 2K 4K BK

FREQENCY [dB]

Fig. 4 Tire/road noise measured 1983 or 1984 on four road surfaces which are

8

Sandberg

80

[dB] TIRES: P,S,M,W,G,GS

_

SPEED: 70 km/h

1983

70'

//'\. .../_j?"

!, ... /f\~\

60

O SURFACES:

5

No.1 Smooth artificial, 71.6 dB(A)

--- No.2 Rough artificial, 75.5 dB(A)

'

--- No.4 Smooth road,

73.9 dB(A)

___... No.5 Rough road,

76.1 dB(A)

40 I I |L I I LI l I T1 I I 1I I l l' l T l| U I L| l l

125 250 500 1K 2K 4K BK

FREQUENCY [Hz]

Elli Tire/road noise on a pair of road surfaces compared with a pair of

artificial test track surfaces

80

[dB] TIRES: P, S, M,W, G, GS

_

SPEED: 70 kmlh

70

60 _

50- SURFACES:

No.1 (1983), 71.6dB(A)

___- No.1 (1984), 72.3dB(A)

40 I I : I I ll I I % H I % r I : I I lr I I 'I l I i25 250 500 IK 2K 4K BK

FREQUENCY [Hz]

f_ig_.__6_ The effect on tire/road noise of painting surface 1-83 three times with