From the October 2016 issue
Your vehicle?s tires are rolling kick drums. Keith Moon played two; your car plays four. Expansion joints, potholes, and heaves pound the rubber, which compresses the air inside and transmits hollow thuds to the cabin.
As cars get quieter, engineers are working to stifle the drumbeat of tire impacts. Their current favored method is polyurethane insulation glued around the tire?s inner liner. These acoustically insulated tires have stealthily spread through the market to the point that they are now offered by all the major tire manufacturers and come installed from the factory on several high-end luxury vehicles, including those hallmarks of tranquility, the Mercedes-­Maybach S600 and the Tesla Model S.
001: Yes, it really is that simple. Acoustically insulated tires use a ring of polyurethane foam bonded to the inner liner to quiet the resonant ping of tire impacts. Or at least that?s the theory.
Tire manufacturers see big potential for the technology as electrification silences powertrains, making tires one of the most obvious sources of sound intrusion. The main function of inner tire insulation is to improve the tire sound quality, specifically by absorbing impact noise. In actuality, it reduces overall cabin volumes only slightly. It has the greatest effect on frequencies near 200 hertz (Hz), a sound that is low in pitch, relative to what the human ear can register, but is at the high end of the frequencies a tire generates. Think of the d...