It is well-known that acoustic modes exist in tire cavities.  Previous research on tire cavity modes has focused on the splitting of this mode owing to tire loading and rotation, and on the transmission of structure-borne noise to the vehicle interior due to force that the tire cavity mode exerts on the wheel hub.  In contrast, here the major concern is the identification of the tire surface vibration and the sound radiation from the tire surface that can be attributed to the tire cavity mode.

The tire cavity mode results from the interference of airborne, acoustical waves propagating in opposite directions within the tire cavity.  Those waves drive corresponding waves in the tire carcass.  Here, the surface normal vibration of a point-driven tire has been measured over a complete circumference by using a scanning laser Doppler vibrometer.  When the space-frequency data is transformed to the wavenumber-frequency domain, a clear feature that can be attributed to the tire cavity mode becomes visible.  Wavenumber filtering (to remove the effect of structure-borne waves in the tire carcass), followed by an inverse transform, reveals the spatial pattern of vibration on the tire surface resulting from the tire cavity mode.  Although the magnitude of the surface vibration resulting from the tire cavity mode is small, its radiation efficiency is high owing to the high phase speed of the acoustic waves that create the tire cavity mode.  It has also been found, that, as expected, tire vibration features associated with the tire cavity mode disappear when the tire is filled with fibrous, sound absorbing material.  The splitting of the tire cavity mode into two modes having slightly different frequencies will also be demonstrated, and the degree of the split will be compared with theoretical predictions.  Finally, measurements of sound radiation from a tire driven by a steady-state, point input, and from a tire driven by a uniform impact over the contact patch area will be presented, and the features associated with the tire cavity mode will be highlighted.