• • The four-DOF model incorporating normal motion eliminates the over-evaluation of system stability present in the three-DOF model, as validated by line testing; this prevents underestimation of chaotic stick–slip risk in high-speed train brake design.
• • Tangential stiffness is the dominant factor inducing chaotic stick–slip vibration in the three-DOF model, whereas in the four-DOF model it primarily modulates amplitude; normal stiffness is identified as the critical parameter driving vibration chaos, necessitating distinct design strategies for each model fidelity.
• • Damping has a minimal impact on the occurrence of chaotic stick–slip vibration, indicating that relying solely on damping adjustments is insufficient for suppression; instead, stiffness and inertia parameters must be prioritized.
• • Optimal ranges for brake disc rotational inertia (5–9 kg·m² and 11–22 kg·m²) and friction pad mass (7–17 kg) effectively mitigate chaotic stick–slip vibration, providing actionable thresholds for industrial brake system design to reduce fatigue wear and enhance service life.