What is the tire friction circle and how is it used in vehicle dynamics?

The friction circle represents the combined limit of longitudinal and lateral tire forces. When braking uses some of the available friction, less is available for cornering, and vice versa. The combined force vector must stay within the friction circle. This concept is used for ABS and ESC calibration, driver training, lap time simulation, and understanding why trail braking works. The actual shape is often elliptical due to differences in peak longitudinal and lateral friction coefficients.