Tyre/road noise measurements on ISO tracks according to the UN ECE Regulation 117 Truls Berge 1 SINTEF Digital, Acoustics P.O.BOX 4760 Torgarden NO-7465 Trondheim, Norway Piotr Mioduszewski 2 Gdansk University of Technology ul. Narutowicza 11/12 80-233 Gdańsk, Poland

ABSTRACT

Within the Polish-Norwegian research project ELANORE, a limited Round Robin Test has been performed on 3 ISO tracks in Northern Europe. The basic objective of the project is to improve the EU directive on labelling of tyres for noise and rolling resistance, and this directive is based on the measurement procedures defined in the UN ECE Reg.117. The same test car, test tyres and measurement equipment as well as personnel were used on all test tracks, to minimize the measurement uncertainties. All tracks were built according to the specification given in ISO 10844:2014. Five sets of C1 tyres were tested. They consisted of 2 sets of summer tyres, one all- season, one winter and one set of the SRTT tyres. Except for the SRTT tyres, the other 4 had labelled noise values from 67 to 74 dB. In addition to the test conditions specified in Reg.117, a modified test was also included, where the load and inflation pressure were adjusted to fit better the test vehicle specifications. Due to some adverse weather conditions at two of the test tracks, only a part of the test program was accomplished. The paper presents results from these measurements. Additional measurements are planned for 2022.

1. INTRODUCTION

Source-related measures as a mean to reduce road traffic noise have been established to be the most cost-beneficial measure, compared to conventional methods, such as noise barriers and/or façade insulation. One of these source related measures is to use low noise tyres. The maximum permissible noise level for the different categories of tyres is defined by the UN ECE Regulation No. 117 [1]. To motivate the use of more environmentally friendly and safe tyres in 2009 European Commission introduced a tyre labelling directive, (EU) 1222/2009 [2], covering three different performance properties of a tyre: rolling resistance, wet grip and sound emissions.

1 truls.berge@sintef.no 2 pmiodusz@pg.edu.pl

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In 2021 this directive was replaced by a new one (EU) 2020/740 [3] with some adjustments, related mainly to the inclusion of snow and ice performance of winter tyres. Figure 1 shows the new version the EU tyre label.

Figure 1: The EU Tyre label valid from 1 May 2021 [3]

This label is the main tool of communicating three of the main performance properties to the consumers, including buyers of replacement tyres. A consumer (end-user) survey in 2016 [4] showed that the safety aspect (wet grip) was most important, followed by the price and then fuel efficiency. The tyre/road noise was only the 4 th (last) most important item. Therefore, it is important to strengthen the importance of the label, especially relating to the noise part.

The consumers thrust in the labelling system is of high importance. If a consumer has a priority of the noise behaviour and chooses a tyre with a class A label value, it is important that the costumer experience this also while in use of the vehicle, even if the tyre label value for noise relates to the external noise of the vehicle and not directly to the noise inside the vehicle compartment. The rolling resistance label value is more directly, but not fully, linked to the fuel consumption of the vehicle in conjunction with the power-train efficiency, road surface and driver behaviour. Wet grip label value directly affects the braking distance of the vehicle on wet road surface as well as on dry to some extent depending on the road surface.

The rolling resistance label is measured in a laboratory condition on a drum equipped with a very smooth surface according to the specifications given in Reg.117. Thus, the label value may not correspond to the behaviour of the tyre on normal trafficked roads.

The noise label value is measured on a smooth dense asphalt concrete surface specified in ISO 10844. This surface was first standardized in 1994 to be used for type-approval of noise emitted by accelerating road vehicles (ISO 362-1). It was designed to give a low contribution from tyre/road noise, as the main focus at that time was on power-unit related sources. However, since this was the only "standardized" test surface, it has also been used in standards and regulations for noise emitted by tyres (ISO 13325 [5] and Reg.117). Several studies have shown that there is a very low correlation between the labelled values and actually measured noise levels on normal, trafficked roads with conventional road surfaces [6, 7].

2. THE ELANORE PROJECT

The ELANORE project (Improvement of the E U tyre LA belling system for NO ise and rolling RE sistance) is an international project carried out by a consortium consisting of Gdansk University of Technology (GUT), SINTEF (Norway) and EKKOM (Poland). It is funded within a joint agreement between Norway Grants and the National Centre for Research and Development

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(NCBIR) in Poland (POLNOR 2019 Call – Energy, transport and climate). The three-year ELANORE project started in 2020.

The main objective of the ELANORE project is to improve the efficiency of the EU tyre label, both concerning rolling resistance and noise. It is organized into the following work packages (excluding administration and dissemination):

WP1 : Study of the representativity of the test methods for rolling resistance, as specified in

Reg.117, compared to measurements on real, conventional roads. This will be done by testing tyres on drum facilities and comparing to real road surface measurements.

WP2 : Study of the representativity of this regulation by comparison of noise measurements

performed on selected test tracks with ISO surface (Round Robin Test) and measurements conducted on trafficked roads in Poland and Norway with typical road surfaces.

WP3 : Proposal of a practical method on rolling resistance measurements that correlates better with

measurements on real roads. An optimal replica of a road surface for drum tests will be developed and an improved test procedure for tyre fuel efficiency labelling will be proposed.

WP4 : Proposal of an improved method of measuring tyre/road noise for labelling purpose. This

will be done by using a modernized CPX trailer both on ISO test tracks and on real roads in Norway and Poland and performing laboratory measurements on roadwheel facility with a drum covered with replica road surfaces.

WP5 : Estimation of the impact on the environment of the proposed improved EU Tyre labelling

procedures for rolling resistance and noise.

This paper deals with the noise part of the ELANORE project only and supplements itself with another paper presented at this conference entitled “Tyre/road noise measurements on ISO tracks using the modified CPX method” [8].

3. FIRST PART OF ROUND ROBIN TEST ON ISO TEST TRACKS

3.1. Test Program

In the summer of 2021, GUT and SINTEF performed noise measurements on 3 selected ISO test tracks in Northern Europe. The following measurement plan was scheduled on each of the test tracks:

- controlled pass-by (CPB) measurements with a passenger car according to the UN ECE

Regulation No. 117 using 5 sets of C1 tyres including one set of SRTT tyres,

- additional CPB measurements with an increased tyre inflation pressure and reduced tyre load

(compared to Reg.117 conditions), named CPB with modified test conditions,

- CPX measurements using a modernized CPX trailer (property of GUT) with both Reg.117

and modified test conditions,

- measurements of texture properties using a texture surface drone.

On one of the test tracks (ISO track 2), EKKOM performed measurements of Sound Exposure Levels (SEL) during the CPB tests, with a microphone located at a height of 4,0 m and at a distance of 10 m from the centreline of the track. These sound levels will be used for later noise modelling using the Cnossos-EU prediction model and are not reported in this paper. Also, the results of CPX measurements are not presented here, but can be found in the supplementary paper: “Tyre/road noise measurements on ISO tracks using the modified CPX method” [8].

3.2. Test Tyres

The tyres selected and used for the purpose of CPB measurements on ISO test tracks are presented in Table 1. The Designation Code is the internal code used by GUT. The tyres with numbers given in bold are the tyres which also were used for the CPX measurements.

Table 1: Description of the selected and tested tyres for controlled pass-by measurements

3.3. Test Vehicles

For all the CPB measurements, the same passenger car – Skoda Superb production year 2021 (see Figure 2), the same driver and same measurement equipment was used. The test vehicle was equipped with a DSG automatic 7 gear box. During all pass-by measurements, the gear lever was set to neutral (N) and the engine was idling.

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Figure 2: Test vehicle: Skoda Superb Combi 2.0 TSI 140 kW (190 HP)

3.4. Test Conditions

Noise measurements were performed with tyre load and inflation pressure according to the values prescribed in the UN ECE Regulation 117 [1] as well as with a modified test condition.

According to the Reg.117, tyre load and inflation pressure depend on the maximum load of the tyre (load index). Using the formulas given in Reg.117, the tyre load was calculated to 530 kg – uniform for all the tested tyres. The inflation pressure was also identical for all tested tyres – was set to 200 kPa in cold conditions.

In the modified conditions it was assumed that the tyre load and inflation pressure depend on the particular test vehicle, in this case Skoda Superb. Thus, the tyre load corresponds to an average load condition of this vehicle: car net weight of 1590 kg (including the driver weighting of 75 kg and 90 % of fuel), plus two passengers (each weighting 85 kg) and 80 kg of luggage. For the used test car the calculated and used tyre load was 460 kg. The tyre inflation pressure should meet the requirements of the vehicle manufacturer. The regular inflation pressure for this Skoda Superb was 230 kPa and this was used during the modified test. Thus, for this test, the tyre inflation pressure was increased with approx. 15 %, while the tyre load was reduced with 13 %.

Test speeds for both CPB measurement conditions were according to Reg.117: a minimum of 4 speeds in the range of 70 to 80 km/h and 4 speeds in the range of 80 to 90 km/h. In addition, the speeds of 40, 50 and 60 km/h were added to the measurement program. The final noise level was calculated from the linear regression line, using the whole range of speeds from 40 to 90 km/h.

3.5. Test Locations

The measurements were conducted on 3 selected ISO tracks in Northern Europe. All 3 test tracks fulfill the requirements of ISO 10844:2014 [9]. The basic data for the selected test tracks were listed in Table 2.

Table 2: Test track information

Test track Year of construction MPD [mm] Absorption α Modelled pass-by level

L crs at 50 km/h [dBA]

ISO track 1 2015 0,59 0,05 62,4

ISO track 2 2015 0,46 0,03 63,9

ISO track 3 2016 0,47 0,04 63,7

The texture properties of each tested ISO test track were measured using the Surface Texture Drone of MüllerBBM. This drone measures the MPD value and the g-factor (averaged over the distance travelled with the drone and over each wheel track). In addition, a noise level at 50 km/h, L crs , is estimated based on the measured MPD value, the g-factor and the average absorption value for the frequencies between 315 Hz and 1600 Hz. The estimation of L crs is based on an equation developed from the Round Robin Test performed by VDA in 2016 [10], but later modified somewhat by MüllerBBM.

3.6. Test Program Completed

Due to some severe weather conditions (rain and wetness of test track), only part of this measurement program was completed, as shown in Table 3.

Table 3: Test program completed, with number of tyres measured

CPB

ISO Test track

Reg.117 Modified

1 5 -

2 5 5

3 2 -

For the Reg.117 conditions, there are 2 tyres which were measured on all 3 test tracks.

4. MEASUREMENT RESULTS

It has already been planned that supplementary measurements will be performed in July 2022 on one more ISO test track in Europe. Thus, in this paper only preliminary measurement results are presented. A final test report will be provided, and complete results will be published and discussed in a reputable journal when the full CPB test program on ISO test tracks has been achieved.

During the measurements, both the air and the road surface temperatures were monitored, not continuously, but only at the start and stop of each tyre measurements program. There is a temperature compensation procedure given in Reg.117. It is based on road surface temperature, while in the ISO standard for pass-by measurements, ISO/DTS 13471-2:2021 [11] the correction formulae is based on air temperature. In Reg.117, there is a different slope below the reference temperature of 20 °C (-0,06 dB/°C) and different above this temperature (-0.03 dB/°C). In the ISO document, there is a linear correction based on air temperature for the whole temperature range (-0.10 dB/°C for dense surfaces like the ISO surface).

Table 4 shows the range of air and road surface temperatures during the tests at the 3 ISO tracks.

Table 4: Temperature range during measurements

Temperature [ °C ] ISO track 1 ISO track 2 ISO track 3

Air 17,3 – 23,8 12,0 – 22,9 16,9 – 17,3

Road surface 24,9 – 41,0 20,2 – 38,4 22,0 – 24,2

4.1. Temperature Correction Procedure Influence

In Figures 3 to 5, the final noise levels at the 3 ISO test tracks for the speed of 80 km/h are presented correspondingly for the uncorrected levels, the corrected levels according to Reg.117 (road surface temperature) and corrected according to the ISO/DTS (air temperature). In addition to the noise level for each of the tyres, the average for the 5 tyres are included.

The figures show that the ranking of the tyres does not change neither with the temperature correction procedure nor by the test track used.

Figure 3: Without temperature correction

No temp correction, 80 kwh

Figure 4: Reg.117 temperature correction

Lamax, dB(A) Seesruaea n % 6 R117 temp correction, 80 km/h 150 track Iso track2 Is0rack3 Yolohama sa Michetin Bridgestone Evergreen sasarr average

Figure 5: ISO/DTS 13471-2:2021 temperature correction

{50 temp cortection, 80ur/h

4.2. Tyre Load and Inflation Pressure Influence

The differences in noise levels obtained under different tyre load and inflation pressure conditions are shown in Table 5. All measurements were conducted on ISO track 2 at the speed of 80 km/h. No temperature correction was applied.

Table 5: Effect of tyre load and inflation pressure on measured noise levels

Tyre Reg. 117

Modified

Difference

[dB(A)]

[dB(A)]

[dB(A)]

Yokohama 72,2 71,8 0,4

Michelin 74,4 74,1 0,3

Bridgestone 73,6 73,3 0,3

Evergreen 73,3 72,9 0,4

SRTT 76,1 76,2 -0,1

For the four standard C1 tyres, the difference between the two test conditions is small, in the range of 0,3 - 0,4 dB. Except for the SRTT tyre, the noise levels are reduced , when testing according to the modified conditions. However, if the air temperature correction procedure is applied, the influence of the modified test changes for the Michelin tyres (level increases for the modified conditions) and the SRTT tyres (level decreases for modified conditions), see Figure 6. Please note that these conclusions are based on one single ISO track.

Figure 6: Temperature correction influence on differences in noise levels due to test conditions

4.3. Test Track Influence

The measured noise levels for the 3 ISO test tracks, including average and spread, corrected for temperature according to the Reg.117, for all tyres tested at the speed of 80 km/h are presented in Table 6.

Table 6: CPB levels at 80 km/h for 3 ISO test tracks according to Reg.117 test procedure

Sound pressure level in dB(A)

80 km/h

Tyre

ISO Track 1

ISO Track 2

ISO Track 3 Average Spread

Yokohama 71,3 72,2 70,0 71,2 2,2

Michelin 73,0 74,4 72,7 73,4 1,7

Bridgestone 72,3 73,6 - 73,0 1,3

Evergreen 72,1 73,3 - 72,7 1,2

SRTT 75,1 76,1 - 75,6 1,0

The average noise levels at ISO test track 1 for all 5 tyres are lower than for ISO track 2. At ISO track 3, the levels of both Yokohama and Michelin tyres are somewhat lower than on other ISO tracks. The obtained spread in noise levels between ISO tracks is from 1,0 up to 2,2 dB (average of 1,5 dB) depending on tested tyres. The highest values are for tyres tested also on ISO track 3. The spread between ISO tracks 1 and 2 only is from 0,9 to 1,4 dB.

4.4. Tyre Ranking

The ranking of noise levels measured according to Reg.117 corrected for road surface temperature and compared to the labelled values are shown in Table 7. The "label values" were calculated based on the measured noise levels during the Round Robin Test.

Table 7: Tyre noise ranking on ISO track 1 and ISO track 2, compared to the noise label values as given by the manufacturer

Manufacturer

Noise level ISO track 1

"Label value"

Position

Noise level ISO track 2

"Label value"

Position

Position

noise label

Tyre

ISO track 1

in ranking

ISO track 2

in ranking

in ranking

value [dB(A)]

[dB(A)]

[dB(A)]

[dB(A)]

[dB(A)]

Yokohama 71,3 70 1 72,2 71 1 67 1

Michelin 73,0 72 4 74,4 73 4 69 2

Bridgestone 72,3 71 3 73,6 72 3 71 3

Evergreen 72,1 71 2 73,3 72 2 74 4

SRTT 75,1 - 5 76,1 - 5 - -

The table shows that the ranking of the tyres is the same on both ISO test tracks based on the measured levels. Furthermore, that the Yokohama tyre is the quietest on both ISO tracks, as well has the lowest label value. The Evergreen tyre has the highest label value given by the manufacturer, however it is the tyre with the second lowest measured noise level. Only for the Bridgestone tyre, there is an agreement with the label given by the manufacturer and the label value on ISO track 1. The highest difference is for the Michelin tyre on ISO track 2, where the label value based on measurements is 4 dB higher than the label given by the manufacturer.

4. CONCLUSIONS

The performed CPB measurements showed that there ranking of noise levels for the 5 sets of tyres was not influenced on the temperature correction procedure chosen. The ranking was also the same on two of the test tracks, where all 5 sets of tyres were measured. The maximum difference between the three ISO tracks is 2,2 dB at 80 km/h. Note that only 2 tyres were measured at all three ISO tracks.

The obtained results give a different ranking of the noise levels compared to the label values given by the tyre manufacturer. The differences in noise label values between the measured during the Round Robin Test and given by manufacturer are up to 4 dB. For the one tyre only both values are the same when tested on ISO track 1. For other cases the obtained values are both higher and lower that labelled.

Except for the SRTT tyres the modified tyre inflation pressure and tyre load slightly reduces the noise levels in the range of 0,3 - 0,4 dB. However, this does not influence the ranking of tyres.

This paper presents preliminary results from a Round Robin Test performed on 3 ISO test tracks. Due to adverse weather conditions, a complete measurement program was completed only at one of the test tracks. When the complete test program has been achieved in 2022, including measurements on trafficked roads in Poland and Norway, the overall results will be analyzed and a proposal for improved procedure for noise labelling of C1 tyres will be presented.

5. ACKNOWLEDGEMENTS

The work of the ELANORE project has been made under the Programme "Applied Research under the Norwegian Financial Mechanisms of 2014-2019 between Norway Grants and NCBR, under the contract No . NOR/POLNOR/ELANORE/0001/2019-00.

6. REFERENCES

1. UN ECE Regulation 117.02, 2011. Provisions concerning the approval of tyres with regard

to rolling sound emissions and to adhesion on wet surfaces and/or to rolling resistance. Regulation No.117 of the Economic Commission for Europe of the United Nations (UN/ECE), Geneva, Switzerland (https://eur-lex.europa.eu/legal- content/en/TXT/?uri=CELEX%3A42011X1123%2803%29)

2. EU, 2009. Regulation (EC) No 1222/2009 of the European Parliament and of the Council of

25 November 2009 on the labelling of tyres with respect to fuel efficiency and other essential parameters., ( https://eur-lex.europa.eu/legal-content/EN/ALL/?uri=CELEX%3A32009R1222 )

3. EU, 2020. Regulation (EU) 2020/740 of the European Parliament and of the Council of 25

May 2020 on the labelling of tyres with respect to fuel efficiency and other parameters, amending Regulation (EU) 2017/1369 and repealing Regulation (EC) No 1222/2009, (https://eur-lex.europa.eu/legal-content/en/TXT/?uri=CELEX%3A32020R0740.)

4. Viegand & Maagøe A/S (2016): Final Report. Review study on the Regulation (EC) No

1222/2009 on the labelling of tyres. March 2016.

5. ISO 13325: 2018, Tyres — Coast-by methods for measurement of tyre-to-road sound

emission. ISO, Geneva, Switzerland.

6. Kragh, J., Oddershede, J., Skov, R., Bendtsen, H., 2015. NordTyre – Tyre labelling and

Nordic Road surfaces – Analysis of data on passenger car tyres . ( http://www.nordfou.org/knowledge/Documents/NordTyre%203%20-%201.pdf , accessed 28.04.2022)

7. Berge, T., 2005. Measurements of tyre/road noise from passenger car tyres according to the

EU-directive 2001/43/EC, on a number of different road surfaces. ( https://sintef.brage.unit.no/sintef-

xmlui/bitstream/handle/11250/2388161/SINTEF%2BA2575.pdf?sequence=3&isAllowed=y. )

8. Mioduszewski P., Berge T.: Tyre/road noise measurements on ISO tracks using the modified

CPX method , Proceedings of Inter-noise 2022, Glasgow, Scotland, United Kingdom, 2022

9. ISO 10844:2014, Acoustics – specification of test tracks for measuring noise emitted by

road vehicles and their tyres. ISO, Geneva, Switzerland.

10. Richartz, G., Männel, M., Wibmer, C., Gmbh, F., 2019. VDA-Study: Round-Robin-Test

Pass-by Noise tracks Europe EXCERPT for GRBP . Task Force on Measurement Uncertainties ( https://wiki.unece.org/download/attachments/92012874/TFMU-01-03%20%28VDA%29%202019-05-

20%20-%20VDA%20-%20Final%20report%20RoRoTe%20Europe_20161103_EN_EXCERPT.pdf?api=v2 )

11. ISO/DTS 13471-2:2021, Acoustics - Temperature influence on tyre/road noise measurement

- Part 2: Correction for temperature when testing with pass-by methods. ISO, Geneva, Switzerland.