An exploratory step for a general unified approach to labelling of road surface and tyre wet friction

Wet skid-resistance is of paramount importance for road safety as it has been recognized to affect wet-road accidents. Recently European Regulations are introducing mandatory classification for tyre friction performance by means of tyre labelling procedure. In this paper an experimental study has been carried out in order to search for a relationship between indexes employed in the tyre and pavement classification. Coupled friction tests have been performed in a controlled manner on five test track with varying texture properties and significant statistical relationship has been derived between Wet Grip Index (WGI), as defined in the European Tyre Labelling Procedure and the International Friction Index (IFI), according to World Road Association (PIARC) friction harmonization experiment. If a temperature correction of skid data is applied a good correlation between WGI and IFI can be obtained. Although the experimental study has to be integrated with a wider measurement campaign, preliminary results seem to indicate that a unified wet tyre-road classification can be pursued allowing a better awareness of the road safety level among road users.