The impacts of tyre hardness and tread depth on tyre/road noise

To explore the impacts of tyre properties on tyre/road noise, a series of on-road CPX tests were conducted on one dense asphalt road surface, named wearing course (WC), and one porous asphalt road surface, named polymer modified friction course (PMFC). Old to new Yokohama tyres with various rubber hardness and tread depths were tested. The tyre rubber hardness was measured according to ISO 868:2003 with a type-A durometer having an in-denter consisting of a truncated cone diameter of 0.79±0.03 mm and at an angle of 35°±0.25°. The CPX tyre/road noise measurements were carried out according to the draft ISO11819-2:2012. The results show that the tyre/road noise at 50 km/h on the WC surface increased with increase in tyre rubber hardness and decreases with the decrease of tread depth. The same phenomenon was observed at 70 km/h for the tread depth but no significant change with the change of rubber hardness was observed. For the PMFC surface, similar results were obtained except that no significant relationship between noise and tread depth can - be drawn for reference at 50 km/h. Spectra analysis shows that rubber hardness has little effect at and around 1000Hz at which the tyre/road noise peaks on the WC surface but tread depth has significant effect around that frequency range. The rubber hardness however shows significant effect around 800 Hz frequency band at which the tyre/road noise peaks on the PMFC surface while the tread depth does not have significant effect.