Abstract: Many tire fault monitors are designed nowadays because tire failure is proved to be one of the main causes of traffic accidents. However, most of them are of high manufacturing cost and unreliable. A new practical tire fault observer is devoted. Based on the introduced dynamic tire/ road friction model that considers external disturbances, the observer estimates and tracks the changes of tire/road friction conditions using vehicle track forces and wheel angular velocity information to carry out tire fault diagnosis. Since the wheel speed sensor is a basic component of normal anti-lock brake system (ABS), the observer proposed could be easily realized in low cost within the anti-lock brake system.