Enhancing wet braking performance: the impact of tire tread material viscoelastic properties and the influence of tread wear

Effective braking on wet roads is vital for ensuring the safety of both passengers and vulnerable road users. When the road surface is wet due to the presence of a film of water that partially covers the pavement texture, the available friction between the tire and road diminishes compared to dry conditions. This reduction can manifest in different ways, from moderate decreases in the tire's ability to transmit tangential forces through frictional interaction with the pavement during light wetting to the more severe loss of contact associated with hydroplaning when a continuous water layer builds up in front and under the tire. To enhance control and safety while driving, it becomes essential to understand the complex mechanisms that affect tire performance in these challenging conditions. This study examines the impact of the tire tread's viscoelastic properties on wet braking performance, also focussing on how changes in these properties due to wear and aging affect braking distances throughout the tire's lifespan. Additionally, the research takes into account the effects of reductions in tread depth and variations in the shape of the contact patch. To this end, experimental data from wet braking tests, conducted according to established regulatory procedures, are complemented by assessments of tire tread viscoelastic properties, contact patch shape characterisation, and tread pattern features. Then, a feature selection procedure is employed to identify the relative importance of the parameters obtained from previous characterisations in predicting wet braking performance. Finally, the study highlights the significant contributions of tire tread viscoelastic behaviour and wear on tire performance in wet conditions. These insights may guide future tire design and regulatory advancements.