‘RATIN’ project reducing car tyre noise
The EU-funded RATIN project is creating a mathematical model of how car tyres produce noise. Team members say subtle changes in both road and tyre design could significantly reduce traffic din.
Noise pollution is a major environmental problem and the European Commission has, for the past 20 years, supported efforts to reduce the clamour caused by road traffic. Much of this has been aimed at reducing vehicle engine noise. Now that engines are quieter, the sound of the wheels on the road accounts for most of the noise made by a car travelling faster than 30 km/h.
Where tyre meets road
As a car moves, the roughness of the road surface causes the tyres to vibrate, producing sound waves. This results in a noise typically described as a roar or a rumble. A separate phenomenon involves air being trapped by the advancing tyre. When the air is forced out of the way it causes a noisy ‘shhhh’ or hiss in a process called air pumping.
According to Roger Pinnington at the University of Southampton’s Institute of Sound and Vibration, significant noise reduction can be achieved by changing the nature of road surfaces. Pinnington is part of the RATIN (Road and Tyre Interaction Noise) project. Launched under the EU’s Fifth Framework Programme (FP5), RATIN is one of the first EU-funded projects to attempt to reduce tyre noise.
"A smoother road is generally quieter than a rough one,” says Pinnington, “but it can be slippery when wet. New research shows that surfaces can be made that are both smooth and porous to water so I suspect this is the direction we may go in."
Meeting new requirements
RATIN represents a direct response to the 2001 EU Directive on motor vehicle tyre noise, which calls for the application of “a realistic, reproducible method enabling the noise arising from contact between tyres and road surfaces to be measured”.
On the basis of such a method, says the Directive, a numerical value could be produced representing sound levels generated by various types of tyres fitted to various types of motor vehicle. The Directive also acknowledges that tyres must be designed both for safety and environmental performance, and that a constraint on one parameter can affect the other.