Brake steer is a metric to measure the amount of self steer generated by a suspension system when it is subject to a braking (longitudinal) load at the contact patch. Brake steer is measured as degrees of toe change per Kilo-Newton of force at the contact patch, Deg/kN.
Brake steer is required to ensure the vehicle is stable under braking. In production vehicles, it is typically tuned to give an understeer tendency from the suspension (toe out on the front axle and toe in on the rear axle). For a brake-in-bend scenario, the understeer tendency will cause the vehicle to widen its line under braking (as opposed to tightening its line).
Production vehicles would typically have brake steers between 0.03 – 0.15 Deg/kN.