Brake distribution

Drifing test, a car specialty in which the casting of braking is key

The brake distribution (also known as distribution or brake compensation) is an adjustment to a vehicle's braking system to improve its efficiency by taking into account the overload generated on the front axle while decelerating.

Equations

Deceleration effect, which generates a turning moment that increases the brake capacity of the front axle, and reduces the rear axle

When a moving car applies its brakes, its speed is reduced caused by the appearance of a friction force contrary to its progress in the contact between its wheels and the road. The value of these friction forces is proportional to the normal force supported by each wheel, which when the vehicle travels on a horizontal road, is equivalent and contrary to its weight. In turn, the distribution of weight between the axles of a car usually depends on the layout of the engine. In the case of cars with a front engine, it is common for 60% to fall on the front axle, and 40% on the rear.

Because the friction forces ${displaystyle FR1=(N1cdot mu)}$ and ${displaystyle FR2=(N2cdot mu)}$ are applied in the contact between the wheels and the road, and that the mass center ${displaystyle c.m.}$ is located at a height ${displaystyle h}$ above, a couple of forces are generated:

${displaystyle M{text{(fr)}}=(FR1+FR2)cdot h}$

Since the car is supported on the road, it cannot rotate around its center of gravity, so two equal and opposite forces are generated. ${displaystyle M1=M2}$such that:

${displaystyle (M1cdot d1)+(M2cdot d2)=M{text{(fr}}}}}}$

Taking into account its meaning, in the front axle ${displaystyle M1}$ a/ ${displaystyle N1}$while on the rear axle, ${displaystyle M2}$ subtraction ${displaystyle N2}$, which implies that:

${displaystyle FR_{text{(single)}}=(FR1+M1cdot mu)}$

${displaystyle FR_{text{(transfer)}}=(FR2-M2cdot mu)}$

Operation

When a car brakes, there is a greater distribution of the car's weight on the front axle, due to the height above the road of the vehicle's center of gravity. This effect of non-uniform distribution of the load on the front axle is greater the greater the deceleration and the higher the center of gravity is located.

For this reason, in all cars the braking systems are more powerful on the front axle than on the rear, since otherwise the braking would be wasted and skidding the rear wheels would run the risk of suffering a spin as little as it turns. In fact, brakes are often designed to lock up earlier on the front axle than on the rear even in the dry, as understeer is easier to fix than oversteer.

To further improve braking, in competition vehicles manual brake distributors are used, since the ideal braking distribution is not always the same, for example, in the wet and in the dry, since the deceleration is different and with it the distribution of weight on the axes.

To obtain the ideal braking distribution in street cars, without having to select it manually, the electronic systems EBV and EBD have been developed in conjunction with ABS.

Motorcycles and bicycles

In the case of motorcycle and bicycle braking, the front wheel receives considerable torque, caused by the weight of the vehicle and the driver. This torque tends to raise the rear wheel and reduce its grip on the road. It can even completely lift it off the ground, even causing a rollover if the front brake is used abruptly.

For this reason, you have to distribute part of the braking to the rear wheel, even though the front can take the full load of braking without approaching the skid limit.

There are also systems that rotate the front brake against the wheel, turning braking torque into a help rather than a problem. This system also has other gyroscopic effects that make the bike more agile when cornering.

Bikes with a rider backrest greatly mitigate rear wheel lift and brake much better than those without.

In the case of motorcycles, especially high-end ones, more and more electronic devices similar to those used in cars that automatically optimize braking efficiency are being incorporated. Earlier, in the 1970s, the Italian motorcycle manufacturer Moto Guzzi and the Brembo company had developed a system called integral braking that used two brake discs in front and one in the rear, the clamping force of which was regulated mechanically.