Brakes - Thermal Exchangers that Reduce Speed

A car's brakes turn drive energy into heat energy in order to decelerate. Not only must they have stopping power, but these essential components must also be able to dissipate heat effectively. 

Construction and Principles 

A car's brakes turn kinetic energy into heat energy to achieve deceleration. The brakes are also responsible for ensuring a car doesn't move when parked. 

The basic components of a brake system involve a control device, which takes the input from the driver, a hydraulic system that relays the control operation, and the actual braking device. Recently, this process has been improved with the introduction of control mechanisms that multiply driver input to increase braking power, and ABS systems that stop the wheels from locking up. 

The brake pedal and the brakes are connected via a hydraulic Line. Since the Pascal principle applies to a hydraulic line, the brake pedal is connected to a large cylinder. The pressure built up at this cylinder is boosted and sent to the brake pad or brake shoes, The pads and shoes are made of high friction materials, and by pressing these against the brake disc or brake drum, kinetic energy is converted into thermal energy, thereby slowing the car down. 

The fluid used in the hydraulic line is not oil and is a specialized fluid made for brakes. Brake fluids must not boil when exposed to the heat of the brakes, and there are various types of brake fluids with various boiling temperatures available. 

As motorway driving has become more common, the front brakes of most road cars have moved from drum to disk brakes. In a disk brake system, braking force is applied on both sides of the brake disks by the brake pads that are supported by the caliper. 

Disk brakes have advanced along with other car technologies, and ventilated disks with improved cooling properties have been developed. Caliper technology has also improved, with traditional floating calipers being replaced by large, high-performance opposed-piston calipers.  

What Makes a Car Stop?

Disk Brakes

Friction is applied to both sides of a metal disk that turns with the wheels. Their major advantage is that because most of the components including the disk itself are exposed to the elements, ventilation and heat dispersion are excellent, making them less prone to overheating. Another benefit of disk brakes is that if they get wet, the water will naturally disperse as the wheel turns, and there will be no significant friction loss. It is easier to perform sensitive control of the brakes through the brake pedal with disc brakes, but the brakes do not multiply its own braking power as in a drum brake, and holding ability when parked is less than that of a drum brake.

Drum Brakes

Braking is performed by pushing brake shoes against the inside of a cylindrical drum that turns with the wheels, Heat dispersion is poor, and overheating occurs much more easily than in disk brakes. Also, if water enters the drum, it takes time to recover friction. However when braking, the rotation of the drum automatically drags the shoes against the friction surface, causing the shoes to bite more, and producing additional braking force. In passenger cars, it is normal for drum brakes to be fitted to the rear wheels, which take less of the braking burden. In larger vehicles, drum brakes are often mounted inside disk brakes

Types of Brake Disks

Solid Disks

This is the most basic type, consisting of a simple metal disk. Heat dispersion is inferior to that of ventilated disks, but low manufacturing costs mean that solid disks are often used in the front brakes of light cars, and also on the rear brakes of four-wheel drive vehicles, where the braking loads are relatively small, Alt disks, including ventilated disks need to be strong against frictional heat and good at dispersing heat, which is why the majority are made from cast iron. 

Ventilated Disks

Two disks are layered together, and there are holes between them to provide ventilation. These were initially developed for racing cars, but are also now common in passenger cars. Compared to solid disks, the surface temperature is reduced by around 30%, increasing resistance to fade, and lengthening brake pad life, the downside is that their double thickness makes them a little heavier.

Advanced Ventilated Disk Types

Cross Drilled Disks

Similar to a ventilated disk, but with additional holes drilled on the disc surface to increase heat dispersion and cooling. These are frequently used in racing cars and high performance sports cars. The holes are also effective at removing the dust created when braking* Another type of disk called a '"slotted disk" has channels machined into its surface to achieve the same effect.

Spiral Fin Disks

Two disks are layered together, with heat-dissipating fins arranged in a spiral shape between them. These fins are designed using numerical analysis of the airflow in the disk, to provide maximum airflow through the disk. As a result, heat is dispersed extremely efficiently as the wheels turn. These disks are used in high-performance sports cars and heavier high- powered saloons.

Types of Caliper


A floating caliper has a piston mounted on one side, which pushes the brake pad against the disk when the brake pedal is pressed. The opposing force presses the brake pad on the other side against the disk's other side. Contact of the pads to the disk is constantly adjusted, and there is no time lag between the actions of the two pads, ensuring an identical braking feel every time. The caliper itself is small and light, and can still provide braking power even if the disc warps from extreme heat. Although they begin to lose effectiveness in sustained racing situations, they present no problems at all for regular driving,

Opposing Piston 

This is a setup in which brake pistons are located on both sides of the disc, to squeeze the brake pads against the disc from both sides. Because this setup makes the calipers larger and heavier, there's little choice but to make the caliper body out of aluminum to reduce weight, which in turn makes it difficult to maintain proper rigidity for the caliper unless it is properly designed. It is very effective in racing on a circuit, but to fully utilize their full potential the brake discs also need to be floating mount discs; otherwise with normal brake discs the heat will distort the disc, putting the it at an angle so that the brake pads cannot properly engage the disc surface. With larger brakes becoming popular, multiple piston brakes with 4 pot and 6 pot calipers having a wider brake pad surface area have also been applied to commercial cars as well. A visibly large, opposed piston caliper peeking out from behind the alloy wheels is a strong indication of the car's high performance. 

Upgrading Your Brakes 

Improving Stopping Power

Improvements in engine output need to be coupled with an increase in braking power. The confidence to really put your foot down can only come from knowing that you are able to stop effectively. However, stronger brakes mean that more effective ways of dealing with excess heat also need to be employed.

Boosting Brake Power & Avoiding Brake Fade

A tuned engine with a higher top speed requires a more powerful braking system that works stronger and is more resistant against brake fade. At the most basic level, brakes can be improved by replacing the brake pads, and at the most extreme level, improvements can entail replacing the entire braking system with a high end system designed for motor racing. Just be sure to remember that the braking systems in racing cars are not necessarily ideally suited for all applications, making it important to select parts that are tailored to your specific needs. Also, bear in mind that larger brake pads or brake calipers will increase the unsprung weight of your car, which can have a negative effect on maneuverability. The golden rule is that brake power should always exceed engine power, but installing too effective a braking system in a lightweight car can cause an unbalance In its driving performance. 

Brake Pads

The most basic components when tuning the brakes are the brake pads, which govern braking power and resistance to brake fade. The range of brake pads on offer is huge, from pads designed for the street to top-end motorsports pads. Each of these has a different optimum temperature at which braking power is greatest, and a different level of heat resistance. Choosing the wrong brake pads for your needs may not give the results you hoped for, and could even have a detrimental effect on how your car drives. Higher-end pads also wear quickly, and increase wear on brake discs due to the increased friction. When changing brake pads, as a rule they should all be changed at the same time to ensure even braking. 

Brake Fluid

This is the operating fluid used in hydraulic brake systems. It has a boiling point in excess of 200º C in order to prevent vapor lock, but it also has extremely high moisture absorbency, meaning that It can deteriorate very easily. Brake fluids are graded by DOT grade. The boiling point increases the higher the DOT grade is, but so does the tendency to absorb moisture, meaning that the fluid will degrade more easily (which lowers the boiling point). For this reason, the DOT 5 brake fluid used in racing cars needs to be replaced often. Be aware that braking power does not Increase with the DOT grade.

Brake Hoses

Brake hoses are the pipes through which brake fluid travels. Normally, they are made from rubber, but hard braking can cause them to swell, reducing responsiveness. This can be avoided by using stainless steel meshed brake hoses. These are Teflon hoses covered! with a stainless mesh sheath that combine the flexibility of rubber with an increased resistance to swelling. They are fitted as standard in racing vehicles to ensure that the brakes are always responsive to driver input.

Brake Disks

The most effective way to increase braking power is to increase braking capacity. This involves using larger diameter disks to create more friction. However, large cast-iron brake disks will increase unsprung weight, which can negatively affect how your car drives, To prevent this, lightweight ceramic and carbon fiber disks are starting to become commonly available. Because brake disks become worn through use, they must be regularly replaced or resurfaced to retain their braking power.


Upgrading brake calipers often involves replacing the entire braking system* Normal calipers press the brake pads against the brake disk from one side, and one way to upgrade them is to replace them with opposed-piston calipers, which presses from both sides. Some production cars now come fitted with brakes that have six pistons, as the larger number of pistons exerts more uniform pressure on the brake pad, increasing braking power. Opposed-piston calipers are made with a mono - block construction, and the high rigidity of the caliper itself provides stable braking even under harsh operating conditions.