Some carmakers claim their vehicles generate equal brake force in the front and back. If so, why do I see more brake dust on the front wheels? In theory, the effect of braking to retard a vehicle's speed must be equally shared by the four wheels. While this implies an equal 50:50 front:rear braking, the actual brake torque that is applied on each brake disc or brake drum need not necessarily be a quarter of the total braking force.
There are a number of reasons for this. First and foremost, the weight of the vehicle carried by each wheel is never identical. In most cars, the left and right load on one axle may be very close or even identical, but this is not the case with front and rear pairs of wheels.
Exceptions to this are vehicles designed for an equal front-to-rear weight distribution like some BMW saloons. That, however, is at the point the car is at a standstill.
Weight distribution will also change in real life, being constantly altered by fuel load and passenger occupancy.
The biggest changes in weight carried by each wheel occur on the move. Known as "dynamic load", during cornering and braking, front-to-rear or even left-to-right, loadings fluctuate drastically.
In braking, weight or load transfer to the front wheels accompanied by an equal load reduction at the rear means the braking torque cannot be equal front to rear. Generating equal braking torque would cause the rear wheels to lock up and compromise overall braking performance.
Logically then, brake pressure on the front wheels will far exceed that on the rear. Electronic Brake Distribution (EBD) systems control brake pressure to produce the optimum braking possible based on each wheel's loading condition at that instant.
Braking torque of 80:20 front:rear, for instance, is not unusual. Prior to the advent of EBD, brake systems were designed with smaller rear brakes and later rear-mounted load-sensing pressure-regulating valves to compensate for weight changes.
Most cars, even those with 50:50 kerb weight distribution, have larger brakes with bigger friction pads in front. All these factors contribute to more brake dust in front.
