There are many factors that combine to make this energy conversion happen, including the brake pedal ratio and brake line diameter. Without getting into too many details, here is a basic overview of how most brake systems work:
The vehicle operator steps on the brake pedal to slow down or stop. The brake pedal lever is connected to a rod that pushes a piston in the brake master cylinder. The master cylinder is filled with hydraulic fluid that gets pushed into the brake lines by the piston. The hydraulic fluid presses against pistons in slave cylinders located on each wheel. The slave cylinders actuate either brake shoes or caliper pads against the brake drum or brake rotor, applying enough force to stop the vehicle.
Here’s where physics comes in. As the brake shoes or pads do their job, the kinetic energy of the vehicle is changed into heat. The biggest enemy to brake pads and brake shoes is heat. As the brake shoes or pads change the car’s motion energy into heat, the brakes get hotter. If they get too hot, they won’t work as well and will experience brake fade. It they get hot enough, the brakes will lose their ability to stop the car because the shoes or pads lose their friction against the drum or rotor. The amount of heat generated by the brakes stopping a car at speed can hit 950°F or more.
To combat brake fade, manufacturers use different materials with higher heat resistance for different applications. These materials that resist degradation at high temperatures include composites, alloys, and even modern ceramics. Some of these materials, especially those used in the higher-performance brake sets, have brake rotors and pads that require some heat in them to have enough friction in the first place. When they are cool, the brakes don’t have enough friction and won’t stop the car as well. These types of brakes are used mostly in race cars and not on cars driven on the street. Using brakes kits with different materials in the rotors, pads, shoes, or drums is one way to improve braking in muscle cars.
The brake pads ride very close to the rotor when they are not in actual contact. This leaves precious little room for cooling. Brake pad materials rely on mostly heat-resistant synthetic fibers to resist heating and brake fade. Ceramics and metal fibers from copper and other soft metals are also used in modern brake pads.
Most cars manufactured during the muscle car era were equipped with drum brakes on all four wheels. Modern braking systems tend to have disc brakes on the front and drum brakes on the rear. More-expensive models have four-wheel disc brakes. Disc brakes do a great job stopping a car and are simplistic in design and maintenance.
Another method to increase the braking in vintage muscle cars is to add disc brakes to the front wheels with parts intended for a similar-model car or from a kit designed by a manufacturer to work with the model of car you are performing the upgrade on. Since the front brakes do 75 to 90 percent of the braking, changing from drum brakes to disc brakes on the front is one of the most effective braking upgrades.
Stability, Steering, and Stopping Distance
Tires are literally where the rubber meets the road. Tires are the link between the vehicle and the road surface, and they are the final piece of the braking system. Tires actually stop the vehicle and play an important role in the change of speed and direction. Because these circular devices are involved in transmitting braking, motion, and lateral forces, any one of these forces can and will affect the others. The Motorcycle Safety Foundation (MSF) teaches its riders about this concept in what it calls “the traction pie.”
The MSF has a traction pie graph that represents the total amount of traction that a tire can have. The pie-like segments define areas for acceleration force, braking force, turning, and a reserve. The four segments of the traction pie are ever changing, shrinking, or growing, depending on the action happening at the time. For example, under strong acceleration, that segment of the pie will be larger. The braking segment will shrink to nearly nothing, and turning will probably be somewhere in size between the acceleration and the braking segments. The reverse would be true if the condition was hard braking instead of hard acceleration.
The MSF goes on to explain that the total traction can be consumed by those three segments when they consume all the reserve. After that point, the tires will lose traction. In this explanation of traction, brakes play a key role in stability, steering, and stopping.
In addition to the various brake components, aftermarket manufacturers often produce their own lines of spindles and steering arms too. Spindles can be purchased that raise or lower the ride height of a vehicle but keep the steering geometry correct.
In a traction pie concept from the Motorcycle Safety Foundation (MSF), a circle that represents the total amount of traction available is divided by forces that consume that traction. Acceleration and braking take a large part of the available traction. Turning consumes some of the traction, and whatever is left over is held in reserve. According to the MSF, a reserve should always be maintained. If the reserve is fully consumed, a loss of traction will result in a skid or a spin.
Engineering Details of Braking Performance
The engineering behind brake performance is much deeper than most motorists realize. A great number of factors need to be considered when designing a brake system for a specific vehicle. The vehicle itself figures into these equations.
“The effectiveness of any brake system depends on factors like the weight of the car, braking force, and total braking surface area,” said Mark Chichester of Master Power Brakes. “You have to factor in how efficiently the system converts wheel motion into heat and how efficiently the built-up heat is removed from the brake system. The buildup and dissipation of heat go a long way toward explaining the major differences between drum and disc brakes.”
Drum brakes are at a clear disadvantage when it comes to dissipating heat. As drum brakes get used hard, the brakes fade because of excessive heat buildup in the drum. The drum absorbs heat until it reaches a saturation point and is unable to absorb additional heat.
With disc brake systems, the rotors are not confined in a tight space; they are exposed to the outside air that provides a cooling effect and helps combat brake fade. Most basic disc brake conversion kits have rotors that are made of cast iron.
Cast iron is inexpensive and has great wear properties. Cast iron is also heavy, so those enthusiasts looking to gain performance by losing weight may want to consider rotors made from other materials, such as ceramic composites. Kits with these ceramic composite brakes are engineered to be heat resistant and able to handle higher compressive loads at higher temperatures.
Force Conversions
To understand how the force from stepping on the brake pedal is converted into pressure at the brake’s friction pad or shoe, some elements of the common components in the braking system must be explained.
The force of a driver stepping on a brake pedal to stop a car traveling at a high rate of speed would need to be tremendous if the force wasn’t multiplied. For instance, a young soccer mom in a 4,000-pound sport utility vehicle (SUV) running down the highway at 70 mph would need to use all 120 pounds of her body weight along with both feet standing on the brake pedal to even start slowing down the vehicle. Using that illustration, it is obvious that multiplying the force applied to the brake pedal is critical when engineering a braking system.
Heat is the enemy of brakes, and one of the key advantages to using disc brakes is that they are more effective in the