It is the front/rear distribution of a car's braking power.
The distribution of a car's braking power between the front and rear wheels. For maximum braking efficiency, brake bias should be set so that all four wheels are held to just before the point of locking-up.
In most cars, including street cars, pressing on the brake pedal applies a little more force to the front brakes than the rear. This is designed to take advantage of the fact that under braking, weight transfers to the front of the car. With lots of weight on the front tires, the brakes can be applied very hard without completely stopping the wheels from rotating. At the same time, the rear of the car tends to get lighter so the rear brakes must be engaged less strongly than the fronts to avoid locking the wheels and possibly losing control. In a racecar, brake bias is adjustable by the driver to compensate for changing conditions.
The front/rear distribution of a car's braking power. For the shortest stopping distance, brake bias should match the car's traction at each end during hard braking brake modulation: the process of varying pedal pressure to hold a car's brakes on the verge of lockup. Ideally, the brakes will unlock with only a slight reduction in the pressure needed to lock them. Typically, however, a considerable pressure reduction is required.
The ratio of braking force of the front end of the vehicle compared to the rear. An excessive brake force at either end of the vehicle can cause the brakes at that end to lock before the other end, often leading to loss of control.