VW Polo manuals

Volkswagen Polo Service & Repair Manual: Tires, Rolling Noises, General Information

Rolling noise perceived by the human ear is caused by vibrations transmitted from the noise source to the ear via the air.
Here we are interested in noises created by certain characteristics of the tires as well as the effects of rolling (noise source).
The cause for the noise generation depends primarily on the combination of road surface and tire.
The surface structure and material of the road surface also have a strong influence on the rolling noise. For example, the noise level on a wet road is substantially higher than on a dry road.
The design of the tread has a great influence on the noise generation. Tires with cross grooves at an angle of 90° are louder than tires with grooves running diagonally.
Small tread blocks are unstable. Due to strong deformation, the air is excited by the rolling tires. Air vibrations occur, which will generate noises.
Wider tires are louder. They require more tread grooves for water displacement. Air is displaced by these tread grooves while rolling, which also cause air vibrations.
Other effects which also have an influence on noise generation:
“Tire vibration” is the main cause of rolling noise. The noise is generated by the excitation of the air column in the grooves.
“Air pumping” is the compression and expansion of air as the contact patch comes in contact with the road surface and the tread blocks are deformed.
Aid to Reasoning of Rolling Noise
Noise generation is created chiefly by tires and the road surface.
Influencing factors of road surface are roughness, structure and material.
Influencing factors for tires fall under different tire and rim widths. A wider tire generates more noise due to its wider contact patch than a narrower tire does, because more air is displaced and a greater “mass” is caused to vibrate.
A wider rim also causes the tire to have a wider contact patch. The effects on noise generation are basically the same as those of a wider tire. In addition, the noise suppression characteristics of the tire can, under certain circumstances, be negatively affected by the wider rim.
The tire rolling noise is significantly noticeable in the rear of vehicles with front engines, because wind and engine noise are less audible in the back.
   
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