Stefanelli, Raffaele (2025) A physics-based approach to tire–road friction modeling with validation in both racing and laboratory environments. [Tesi di dottorato]

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Abstract

In the world of motorsport, identifying and maximizing vehicle performance is essential to achieving the best possible results on track. This goal is influenced by a wide range of factors, many of which are difficult to isolate and analyze individually. Among them, friction at the tire–road interface plays a crucial role. From acceleration and braking to cornering and stability, the forces that govern vehicle motion all originate within a small and complex contact region between rubber and asphalt. The ability to accurately model the mechanisms of tire–road friction is therefore fundamental for predictive simulations, control system design, compound optimization and performance evaluation. Yet, despite decades of research, it remains one of the most challenging and debated problems in both scientific and industrial communities. This thesis proposes a physics-based modeling framework that aims to predict frictional behavior starting from measurable and physically meaningful quantities. By integrating three interdependent domains, surface roughness characterization, viscoelastic behavior of rubber compounds and tire operating conditions, this work provides a physically interpretable methodology to estimate friction through a local contact mechanics approach. A key concept is the use of the real-to-apparent contact area ratio ($A_c/A_0$) as a bridge variable that links surface texture, rubber properties and contact dynamics. To support this framework, the thesis also presents a comprehensive study and analysis of both road roughness and rubber viscoelasticity. For the surface domain, dedicated procedures are presented for acquiring and processing surface texture, including experimental scans and a novel image-based reconstruction technique. In parallel, the viscoelastic response of tire compounds is investigated through systematic analysis of frequency- and temperature-dependent behavior, covering key phenomena such as the time–temperature superposition principle and other material non-linear effects. These methodologies are designed to provide reliable input data to the model and to ensure consistency across different compounds, surfaces and operating conditions. Building on these foundational characterizations, the proposed modeling approach is then validated through a dual experimental strategy, combining indoor controlled friction testing and outdoor telemetry data-based grip estimation. This extensive validation ensures robustness across a wide range of surfaces, compounds and vehicle scenarios. Unlike non-physical approaches, the methodology developed in this thesis emphasizes transparency, interpretability and extrapolation capacity, allowing it to be deployed in design, simulation and trackside engineering applications. The resulting model offers a versatile tool for tire manufacturers, motorsport engineers and researchers aiming to understand, predict and optimize tire–road interaction under real-world operating conditions.

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