| Tyre noise that can be heard by the human ear is caused by vibrations which are transmitted by the air from the source of the sound to our ears. |
| Of interest here are the noises caused by certain characteristics and effects while the tyres are rolling (sound source). |
| The noise level will chiefly depend upon the road surface/tyre combination. |
| The surface structure and the road material will have an effect on the tyre rolling noise. The sound level on a wet road, e.g., is considerably higher than on a dry road. |
| The tyre tread has a great influence on the noise. Tyres with transversal grooves at a 90° angle are noisier than tyres with grooves at oblique confluent angles. |
| Small tread blocks are unstable. Their highly pronounced deformation agitates the air as the tyres roll. This creates the air vibrations that cause tyre noise. |
| Wider tyres are also noisier. More grooves are required in the tread pattern to allow the water to drain off. As the tyres go round, the air is dislodged towards these grooves, resulting in air transmitted vibrations. |
| Other aspects with an effect on the emission of sound: |
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| Tyre vibrations are the main cause of tyre rolling noise. They are the result of the excitation of the column of air in the tread grooves. |
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| „Air pumping“ is the compression and dilation of the air as it passes over the support surface of the tyre, due to the deformation in the tread blocks. |
| Theories behind tyre rolling noise |
| The noise is essentially caused by contact between the tyre and the road surface. |
| The determining factors of the road surface are the roughness, structure and material. |
| The determining factors of the tyre include the width of the tyre and of the tyre rim. A wider tyre is noisier, due to the increased contact surface area, as more air is dislodged a greater „mass“ is made to vibrate than in a narrow tyre. |
| A wider wheel rim also implies a wider tyre contact surface area. The effects on the noise are, therefore, basically similar to those of a wider tyre. In addition, a wider wheel rim may result in negative influences on the shock absorbing properties of the tyre. |
| Tyre rolling noises are heard more clearly in the rear seats of the vehicles with engines at the front, as the sound of the wind and the engine muffle the tyre rolling noises. |
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