# Engineers tread toward a quiet tyre

Engineers at Purdue University have developed a new technique for analysing tyre vibrations by creating a ‘fingerprint ‘ that identifies which features produce the most noise.

‘Most of the environmental noise nuisance from interstate highways is tyre noise,’ said Stuart Bolton, a professor of mechanical engineering at Purdue University, West Lafayette. ‘If you are anywhere near an interstate, much of the noise that you hear is generated by the tyre-road interaction, with the exception of some noise from heavy trucks. ‘

A tyre’s tread contains block shapes that strike the road surface like tiny hammers. Those tread blocks and underlying reinforcing belts vibrate and radiate energy outward, producing sound.

Bolton and graduate student Yong-Joe Kim are using a mathematical model to identify which parts of a tyre produce the most noise. The vibrations are characterised on a graph, a visual representation that’s like a fingerprint of each tyre’s vibration pattern.

‘We created this numerical model that we can pretend is a tyre, giving it the properties of a tyre and running a ‘test’ in the computer as if we were doing a real experiment,’ said Bolton. ‘This illustrates the fact that you can predict the vibration and noise differences related to various design features.

Tyre noise and vibration are both a nuisance and a consumer issue because they account for much of the unwanted noise heard inside a car, as well as outside, Bolton said.

The engineers measure various vibrational waves that travel along a tyre’s treadband, which is the outer segment of a tyre that includes reinforcing belts and the tread pattern that meets the road’s surface.

Specific vibrations are assigned ‘wave numbers,’ and those numbers are then used to create graphs that illustrate which vibrations are coming from which portions of the tyre, and which vibrations are likely to produce the most noise.

‘I won’t claim to have totally succeeded in that,’ Bolton said. ‘This is the first attempt to form some simple theoretical models.’

The analytical model represents the treadband as a flat belt connected at both ends to form a circle. However, to be more accurate, the entire tyre – not only the treadband – should be modelled in a three-dimensional cross section, Bolton said.

‘We are working to make the model much more tyre-like,’ he said, concluding that engineers will use findings from such models to help design quieter tyres.