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A lot of efforts were made in the last two decades to lower the tire/road noise. The tire industry has optimized the tread pattern as the main influence parameter so that nowadays the radiated sound pressure of a modern tire in the far field is very close to that of a blank tire with the same construction. Because the tread pattern is needed to achieve the required safety level further noise reduction has to be addressed mainly by tire construction. For many years tire manufacturers have been searching for a construction, which fulfils the targets of the automotive industry and generates less noise. The research was done not only in house but also with public projects. In the EC Project SILENCE a subproject has provided design solutions and hardware solutions for noise reduction, with respect to vehicle/tyre/road integration, under typical urban and suburban traffic conditions. This improvement is based on an increased understanding of noise generation and radiation mechanisms gained by the further development of experimental and simulation techniques. A series of low noise tyres (prototypes) has been developed and tested on a selection of appropriate low noise road surfaces.

The tire is the only part of a vehicle that must be originally and primarily designed to transmit forces to outside the vehicle, and the amount of energy a tire consumes per kilometer in operation and for production has to be minimized. The tire manufactures are searching for many years for a construction, which fulfils the targets of the automotive industry and generates less noise. On dry, wet and snow-covered roads, the safety of traffic can only be ensured by sufficient capability for acceleration and braking deceleration, cornering stability, tracking on acceleration and braking, steering precision and direction stability. The high requirements on safety, economy and durability limit the possible reduction in the emission of tire/road noise.

To understand the noise source mechanism of tire/road noise better than in the past, it is essential to look at the complete sound field of a tire. In the technique of spatial transformation of sound fields (STSF), the Helmholtz integral equation is combined with the acoustical near-field holography. Thus it is possible to analyze the noise source in great detail and to calculate the sound in the far field. A drawback of the acoustical holography is that only planar views of the sound field can be calculated. One method to overcome this limitation is to combine the measurement results of STSF with the inverse boundary element method. By modeling the surface of the tire with boundary elements, the velocities on each element can be identified. First results will be presented. Comparing the sound field of a standing tire excited by a shaker with the sound field of a tire on a drum, it is possible to extract the part of the sound field that is caused by the geometry on the tire only.

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