Tire noise is an important issue both in the vehicle interior and to the vehicle exterior, since it affects passenger comfort and environmental noise levels, respectively. Such noise is increased when a tire encounters discontinuities on the road surface, the discontinuity being either a
gap or a bump. The relatively high frequency (e.g., approximately 1 kHz and above) airborne tire noise generated by such discontinuities is defined as tire slap noise in this study.

Most previous research on noise generated by surface discontinuities has been focused on lower frequency tire noise, typically below 600 Hz, and, in particular, on structural-borne noise transmitted from the tire into the vehicle associated with the acoustic modes of the tire interior.
Here, instead, the focus is on higher frequency airborne transmission. Further, the study here is conducted from the perspective of tire structural vibration, which concerns the vibration of and sound radiation from the tire treadband structure, rather than tire pattern noise, for example.

The high-frequency tire slap noise was investigated in a laboratory environment. The measurements were conducted by using the Ray W. Herrick Laboratories’ Tire Pavement Test Apparatus (TPTA), on which a loaded tire can be run on realistic road surfaces at speeds up to 50 km/h; the resulting tire noise was measured using the On-Board Sound Intensity (OBSI) method. A gap between two different concrete surfaces was chosen as the road discontinuity, and both narrow band and one-third-octave band spectra were recorded over the gap and over
the adjacent smooth road surface segments.

Several tires were tested on the TPTA, and their slap noise was recorded. Surface noise and slap noise were compared up to 1600 Hz to show the impact of the discontinuity on the tire noise radiation. Generally, slap noise is of a higher level than the surface noise, especially between 800 and 1400 Hz, but some tires showed distinct differences between the noise response on the surface and over the gap, while other tires radiated similar noise on both the surface and over the gap. Moreover, static tire mobility measurements were performed to investigate the wave type responsible for the different responses on the gap and the surface.

Cao, R. and Bolton, J.S., Tire Science and Technology, TSTCA, Vol. 46, No. 1, January-March 2018, pp. 38-52

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