Tires are integral to the basic functions of an automobile, i.e., driving, turning and stopping. A variety of key factors are considered in tire development. Recently, attention has focused on improving performance in terms of the sensory comfort felt by people riding in a car. R&D into how tires make sound is a part of the sensory field of science.
A developer of Bridgestone’s flagship comfort tire says “Everyone knows that the sounds heard inside a car change when driving, depending on the road surface. On a rough road, for example, the tires vibrate with a ‘roaring’ sound, and on a smooth road, they make a high-pitched ‘hissing’ sound. Our research focuses on which sounds are the most pleasing to passengers.”
Human beings can hear sounds in the 20Hz to 15,000-20,000Hz range. However, some frequencies are disconcerting to the human ear. Researchers are working to change these frequencies made by tires into more pleasant sounds with cutting-edge technologies. Bridgestone spends considerable time testing the sounds made by tires, adjusting their materials and structures and the design of grooves.
He also says “For example, the ‘roaring’ sound is in the 160-200Hz range, and sounds like trees shaking in hurricane-strength winds. The ‘hissing’ sound is around 1,000Hz, which is the beeping sound made by older phones when you forget to put the receiver back in the cradle. Neither sound is that pleasing to hear. Vibrations from tires create sounds around the 50Hz frequency that can be heard inside the vehicle. This sounds like the humming motor of a refrigerator. These sounds can negatively impact your mood when you become aware of them. Our job is to adjust these sounds made by tires. The world of creating sound is quite complex. We are aiming to make it as quiet as possible. However, it is not our ultimate goal to make a perfectly silent tire because the sound also serves to inform the driver about road conditions. Tires are often compared based on their grip, fuel economy and environmental performance. If more attention was paid to the sounds tires make, I believe people would choose tires that make driving more fun, by producing sounds that do not interrupt conversations inside the car.”