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ROAD NOISE

ROAD NOISE PIRELLI FINDS OUT HOW TYRES AND SURFACES INTERACT Noise is becoming an important issue reduction of the noise generated by rear tyres is possible. in the environmental assessment of highways. In The Netherlands, for The problem is that everything example, profiled road markings are done to reduce noise also has a banne d because, despite their negative effect of some other contribution to road safety, they importan t aspect of a tyre's generate too much noise. Within performance. A reduction in the Europe, permitted noise levels have number of transverse grooves also been reduced steadily over the last reduces traction and increases braking two decades, and it seems that the time. Shallower grooves give lower strict rules now in force may be mileage performance, and more tightened even further. connecting ridges reduce traction as the tyre wears down. In 1974, the EC permitted a noise level of 91dB, but by 1980 this had The tread pattern is not the only To overcome these problems Pirelli been reduced to 88dB. Current codes factor. Tyre compounds also affect has devised its own tests based on allow only 84dB, and the European noise. A softer compound is quieter, sound intensity rather than simple Commission is currently considering but gives a shorter working life and maximum sound pressure, and are following the lead given by Austria also reduces the stability of the conducte d indoors to improve and reducing this to as little as 80dB. vehicle. A more hysteretic compound repeatability. Remembering that noise is measured (one with a greater energy absorption The results obtained are not on a logarithmic scale, and that each ability) is also quieter, but increases 3dB reduction is effectively a halving directly equivalent to those that fuel consumption as a result of its of the noise level, leads to an would be achieved under "real" road higher rolling resistance. appreciatio n of the practical conditions, but the engineers have Different road surface materials difficulties of achieving these targets. found that the figures obtained can also produce different amounts of be easily translated into expected Vehicle noise comes mainly from noise. Proponents of pervious actual noise values by simply the engine and the tyres. The engine macadam use its noise reducing multiplying by a known constant. properties as much as its drainage tends to be the main generator of Measurements are fast, and the capabilities to promote the material. noise, but in a coasting mode the tyre differences caused by small variations noise can predominate. Research into Pirelli has found, from standard in the type of tyre tested can be tyre noise concentrates on trucks rolling vehicle tests conducted at distinguished. rather than lighter vehicles, for 60km/h, that pervious macadam (or obvious reasons. drained asphalt) generates a noise level of between 71 and 74dB. This One of the problems with Four Mechanisms compares with 72-75dB from smooth investigating noise is the actual asphalt, 73-76dB from rough asphalt, testing. The standard noise test, ISO There are four main noise-generating 362, only covers accelerating vehicles an d 76-79dB from concrete mechanisms in tyres: the impact of pavements. which is the worst case for total noise. individual tread blocks; the pumping However, in an accelerating vehicle of air as the tread pattern is Just as with the tyre design, there the engine noise can drown out the compressed; slipping under the are other factors which affect the tyre noise. footprint of the tyre; and vibrations choice of road surface. The major of the tread blocks. drawback with pervious macadam is Anothe r difficulty, which is its shorter working life. common to all scientific experiments, Clearly, the tread pattern of a tyre is that of reproducability. No test can is an important aspect of the study of Pirelli's ambition is to produce a be considered valid unless it can be noise. Using a slick tyre as a control, tyre which is both safe and silent by repeated by another scientist at the base level of noise is about squeezing every last decibel out of another location and produce similar 72.5dB. Typical front tyres generate existing tyre technology. results. With the standard test there about 74dB, meaning that it is are too many variables — weather, unlikely that much decrease can be road surface, vehicle type, etc — to achieved. Rear tyres, which contribute A fuller report may be found in World allow any repeatability in the more to traction, generate about Highways, November 1991. measurement of tyre noise. 76.3dB. Therefore some slight 6 Industrial Lubrication and Tribology Vol. 44 No. 2, 1992, p. 6, © MCB University Press, 0036-8792 http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Industrial Lubrication and Tribology Emerald Publishing

ROAD NOISE

Industrial Lubrication and Tribology , Volume 44 (2): 1 – Feb 1, 1992

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Publisher
Emerald Publishing
Copyright
Copyright © Emerald Group Publishing Limited
ISSN
0036-8792
DOI
10.1108/eb053414
Publisher site
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Abstract

PIRELLI FINDS OUT HOW TYRES AND SURFACES INTERACT Noise is becoming an important issue reduction of the noise generated by rear tyres is possible. in the environmental assessment of highways. In The Netherlands, for The problem is that everything example, profiled road markings are done to reduce noise also has a banne d because, despite their negative effect of some other contribution to road safety, they importan t aspect of a tyre's generate too much noise. Within performance. A reduction in the Europe, permitted noise levels have number of transverse grooves also been reduced steadily over the last reduces traction and increases braking two decades, and it seems that the time. Shallower grooves give lower strict rules now in force may be mileage performance, and more tightened even further. connecting ridges reduce traction as the tyre wears down. In 1974, the EC permitted a noise level of 91dB, but by 1980 this had The tread pattern is not the only To overcome these problems Pirelli been reduced to 88dB. Current codes factor. Tyre compounds also affect has devised its own tests based on allow only 84dB, and the European noise. A softer compound is quieter, sound intensity rather than simple Commission is currently considering but gives a shorter working life and maximum sound pressure, and are following the lead given by Austria also reduces the stability of the conducte d indoors to improve and reducing this to as little as 80dB. vehicle. A more hysteretic compound repeatability. Remembering that noise is measured (one with a greater energy absorption The results obtained are not on a logarithmic scale, and that each ability) is also quieter, but increases 3dB reduction is effectively a halving directly equivalent to those that fuel consumption as a result of its of the noise level, leads to an would be achieved under "real" road higher rolling resistance. appreciatio n of the practical conditions, but the engineers have Different road surface materials difficulties of achieving these targets. found that the figures obtained can also produce different amounts of be easily translated into expected Vehicle noise comes mainly from noise. Proponents of pervious actual noise values by simply the engine and the tyres. The engine macadam use its noise reducing multiplying by a known constant. properties as much as its drainage tends to be the main generator of Measurements are fast, and the capabilities to promote the material. noise, but in a coasting mode the tyre differences caused by small variations noise can predominate. Research into Pirelli has found, from standard in the type of tyre tested can be tyre noise concentrates on trucks rolling vehicle tests conducted at distinguished. rather than lighter vehicles, for 60km/h, that pervious macadam (or obvious reasons. drained asphalt) generates a noise level of between 71 and 74dB. This One of the problems with Four Mechanisms compares with 72-75dB from smooth investigating noise is the actual asphalt, 73-76dB from rough asphalt, testing. The standard noise test, ISO There are four main noise-generating 362, only covers accelerating vehicles an d 76-79dB from concrete mechanisms in tyres: the impact of pavements. which is the worst case for total noise. individual tread blocks; the pumping However, in an accelerating vehicle of air as the tread pattern is Just as with the tyre design, there the engine noise can drown out the compressed; slipping under the are other factors which affect the tyre noise. footprint of the tyre; and vibrations choice of road surface. The major of the tread blocks. drawback with pervious macadam is Anothe r difficulty, which is its shorter working life. common to all scientific experiments, Clearly, the tread pattern of a tyre is that of reproducability. No test can is an important aspect of the study of Pirelli's ambition is to produce a be considered valid unless it can be noise. Using a slick tyre as a control, tyre which is both safe and silent by repeated by another scientist at the base level of noise is about squeezing every last decibel out of another location and produce similar 72.5dB. Typical front tyres generate existing tyre technology. results. With the standard test there about 74dB, meaning that it is are too many variables — weather, unlikely that much decrease can be road surface, vehicle type, etc — to achieved. Rear tyres, which contribute A fuller report may be found in World allow any repeatability in the more to traction, generate about Highways, November 1991. measurement of tyre noise. 76.3dB. Therefore some slight 6 Industrial Lubrication and Tribology Vol. 44 No. 2, 1992, p. 6, © MCB University Press, 0036-8792

Journal

Industrial Lubrication and TribologyEmerald Publishing

Published: Feb 1, 1992

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