Tire-road noise (rolling noise)
Tire-road noise is understood as the interaction between the tire and the road surface. This tire-road interaction contributes in various ways to the generation of road noise. Accordingly, the composition of the effect is complex. The mechanisms of generation vary significantly depending on speed, tire characteristics, and road surface conditions, thus altering the acoustic signature of the tire-road noise in the frequency range.
Vibration noise: The tire is excited differently depending on the speed and surface texture of the road. In vibration noise, a distinction is made between an impact and an adhesion mechanism. The impact mechanism consists of the meeting of the tire tread blocks with the road surface.
The adhesion mechanism is described by a "stick-slip" mechanism and a "stick-snap" mechanism. In the "stick-slip" mechanism, individual parts of the tire are excited tangentially to the surface due to the rolling of the wheel. This leads to an excitation of the tire (vibration) through the sticking of the block on the surface ("stick") and the subsequent release ("slip"). This primarily manifests as tangential movements in the tire. The "stick-snap" mechanism can be understood as the "sticking" and "adhering" of the tire to the surface.
Vibration noise generally has a higher frequency at higher speeds and a fine surface texture (short wavelength) than at low speeds and a rough surface texture (long wavelength). On fine road surfaces, there can also be increased sticking forces (stick-slip) between the tire and the road surface, which become noticeable in the high frequency range.
Cavity resonances: With a certain excitation of the tire by the road surface, eigen resonances can occur in the tire. The natural frequency of a tire is around 220 Hz. Through harmonic vibrations, this can also radiate into higher frequency ranges.
Airflow noise: In the contact zone between the tire and the road, air is sucked in and pressed out due to the tire profile and tire movement ("Air-pumping"). This primarily manifests as medium to high-frequency hissing noises. Additionally, the profiling on the tire can lead to resonances at the profile.
Quiet surfaces with good accessibility to the surface pores allow the air that is pressed between the tire and the road surface to escape more easily. This effect is reflected in a reduction of tire-road noise in the high frequency range.
Horneffect: The tire forms a sound funnel together with the road surface at the front and back. The horn effect leads to sound amplification. Depending on the tire width, the horn effect occurs from about 500-700 Hz up to a maximum of about 1500 Hz.