Increase of noise levels in urban and suburban areas is a major concern for cities today. Much of this noise comes from road traffic. Tyre/road contact noise is a main contributor to road traffic noise and has therefore become a main target for reducing urban noise. Tyres in the European market today must comply with noise limits fixed by European Directive 2001/43/CEE. An important discussion is taking place today about the revision of noise limits. This paper aims to give some light to this discussion in terms of technology solutions for passenger car tyres and expose Michelin point of view about tyre/road noise reduction. The first part of this article reviews the three most influent factors on tyre/road noise levels for a given vehicle today: 1. Road surface: with differences up to 10 dB(A) for different surfaces found currently in Europe 2. Speed: allows in average, on ISO10844 surface, a 4 dB(A) reduction for a 20 km/h decrease. 3. Tyre: can make up to 2 dB(A) variation on noise for the same size and category (both fixed for each vehicle by car manufacturer to meet specific customer requirements) The second part of the article tries to give an overview of relevant tyre parameters for noise and the trade-offs they involve. This is made by means of reviewing the main tyre parameters that can be used to reduce noise. The consequences on other tyre features of a 3 dB(A) noise reduction by playing on each parameter are presented: Reduction by tread pattern design involves a change on tread void ratio from 34 per cent to 0 per cent (slick tyre) with obvious consequences on aquaplaning (60 per cent on curve) and wet braking (40 per cent on low micro and macro texture surfaces). Reduction by tread material stiffness will divide life time of tyre by two by accelerating tread wear. Faster wear involves environment prejudice through twice more waste of tyre carcass. Softer material will also involve important decrease on dry handling and therefore safety. Reduction by tyre structure is today already applied in most current tyres. It is possible to increase noise by 3 dB(A) with stiffer structure but it gets difficult to further reduce noise by reducing structural rigidity while keeping sufficient endurance and handling. Tyre manufacturers keep constant effort to reduce noise motivated by regulations, car makers demands for interior noise reduction (that benefit also exterior noise) and environmental concerns. A tyre/road system approach is now necessary to allow ambitious further noise reduction of road traffic noise in a total performance trade off (A). For the covering abstract of the conference see ITRD E212343.
Samenvatting