Prediction of Split in Fundamental Air-Cavity Mode of Loaded Tires based on Experimental Observations and Computational Simulations

In previous studies, it was found that a tire's fundamental air-cavity mode, typically near 200 Hz for current passenger car tires, splits into two features when the tire is loaded. Since the deformed tires is no longer geometrically symmetric, separate fore-aft and vertical modes appear, the former mode appearing at a slightly lower frequency than the vertical mode. These modes are key contributors to dynamic loads on the suspension system and consequently on cabin noise at around 200 Hz. In this context, measurements of the dispersion relations for a large set of loaded tires were performed to investigate the range of magnitudes of the modal frequency split. Also, finite element analysis of a sub-set of tires was deployed to model the dispersion in the vicinity of the fundamental air cavity mode. Splits ranging from 4 Hz to 14 Hz at rated load have been identified, and it has also been found that the magnitude of the frequency split for a given tire is very nearly quadratically proportional to the applied load. Furthermore, a large dynamic load and noise level can be anticipated when the vertical acoustic mode coincides with a treadband mode having a maximum at the top of the tire.