Abstract: A brake control system for vehicles in which the difference in speed of rotation of a corresponding pair of wheels is detected in a prebraking mode of operation. If the difference in rotational speed exceeds a predetermined amount, the brakes on the pair of wheels are disabled. In one embodiment of the invention, the prebraking rotational speed ratio of the pair of wheels is determined by a comparator and electronic voltage control circuit, and the electrical output thereof fed to a valve control circuit for controlling the brake valves to maintain the braking rotational speed ratio of the wheels substantially equal to the prebraking rotational speed ratio.