Brake bias is the balance of braking force between the front and rear axles. It is a fundamental part of how a car stops safely, and it is deliberately tuned toward the front. Here is what brake bias means.
The front-rear split
Brake bias describes what share of the total braking each axle does. Because weight shifts forward under braking - see why front brakes wear faster - cars are set up front-biased, with the fronts doing the larger share so the rears do not lock up first.
Why front bias keeps you stable
If the rear brakes did too much, the rear tires could lock before the front - and locked rear tires make a car spin. Front-biased braking keeps the rear planted and the car pointing straight, so bias is a safety design, not just a wear factor.
How bias is controlled
Automakers set bias with different front and rear rotor and caliper sizes and with a proportioning valve or, on modern cars, electronic brake distribution; see brake proportioning valve. A failed valve can throw the balance off and cause the rears to grab or fade.
Why it matters for service
Keep both axles healthy so the designed bias holds - worn rears or a dragging caliper upset the balance; see one brake running hot. Use quality matched pads and hardware front and rear.