Tread rubber hardness and tread wear during a tire’s life have a counterbalancing effect on each other, according to a study by Hong Kong Polytechnic University.

The study, “the impacts of tire hardness and tread depth on tire/road noise,” used four Yokohama tires produced in 2007 for its testing. All tires came from the same batch and were measured at varying hardness and tread depths. Additionally, tests were conducted on a dense asphalt and porous asphalt test track instead of in a laboratory.

The findings, which were presented at the ICSV 20 congress in Thailand, concluded that as tread rubber becomes harder there is increased rolling noise, but reduction in tread depth counteracts this, causing a reduction in rolling noise. The study concluded that shallower tread depth both cancels and does not cancel out rolling noise causes by rubber hardening, with results contingent on speed and road surface.

The results showed noise rose on the dense asphalt at 50km/h as tire rubber hardened and decreased in tread depth. The same was observed at 70 km/h for tread depth, but with no significant change for rubber hardness. Similar results were observed on the porous surface, except there was no significant relationship between noise and tread depth at 50km/h.

Rolling noise peaked at around 1000Hz on the dense asphalt surface, with rubber hardness having little effect at this frequency and tread depth having a significant effect. Tests on the porous asphalt surface showed a peak in rolling noise at around 800Hz, and at this frequency band rubber hardness showed a significant effect, but tread depth did not significantly effect frequency, according to the study. (Tyres & Accessories)