In physical terms we can state that energy is the power to do work. When a car comes down a straight line at 300 km/h or more, that car has lots of kinetic (movement) energy. Due to the fact that energy does not get lost, but can only be transformed one kind into another, at braking most of the kinetic energy is transformed into potential energy, more specifically warmth. Formula One cars must sometimes decelerate in a matter of seconds from 350 km/h to about 70 km/h. This procedure generates enormous heat, resulting in brake temperatures up to 1000°C, where on the end of the straight, right before braking, that is nearly 400. That 1000°C occurs at the end of the braking, and is about the highest temperature a carbon brake disc (as they are used in F1, and limited to 28mm thickness and 278mm diameter by the FIA) can take.
Facts and figures
A mere 4 seconds is the amount of time it takes for a Formula One car to go from 300km/h to a complete halt. At 200 km/h, a Formula One contender requires just 2.9 seconds to stop completely, a process that will have been accomplished over 65 meters. At 100km/h, these values are just as mind-blowing: 1.4 seconds and 17 meters! Under these heavy braking periods, a driver is subjected to a horizontal deceleration of close to 5,2G.
The only configuration that allows this performance at the moment is a brake disc/caliper combination of carbon fibre. Its crude performances fast decelerations while its weight allows for each break-disk to remain below the1 kg/each mark. Furthermore, its capacity to take on and dissipate heat provides unequalled longevity: even when heated to over 1000°C prior to cornering, about 800 times per race, the carbon-fiber will last for the duration of a Grand Prix event without complaint. Steel, used until the 80's, was abandoned without any regrets and the overall performance in F1 came out on top.
”The use of carbon-fibre brakes requires a little time to get used to,” states Jarno Trulli. “In fact, during the first milliseconds after pressing the brake-pedal; it feels like nothing is happening.” This delay is in fact the length of time required by the disk/caliper tandem to reach operating temperature, which increases by 100°C per tenth of a second for the first half-second of braking, after which it can reach up to 1200°C. After that short period, deceleration is immediate, and brutal.
From within their cockpits, drivers can adjust the distribution of braking power between the front and rear of their contenders.This influences the handling of the car. Generally speaking, the front has a priority to within a 51% to 60% margin, depending on track conditions. During a race, reducing the rear braking power allows for reduced rear tyre-wear and thus influences the traction.
General construction
The most important elements of a brake system is the brake disc, rotating at the same speed of the wheel. Today, these are made from carbon, while CART still uses steel brake discs. This material is responsible for the brake power advantage Formula one has to CART. The brakepad with brake blocks are located aside and around the brake disc. When the driver pushes the brakepedal, the blocks are pressed against the brake disc, which slows and heats up according to the friction that occurs (dependent on the brakepower the driver asks by pushing the pedal down).
The rotating discs are gripped by a calliper which squeezes the disc when the brake pedal is pushed. Brake fluid is pushed into pistons within the calliper to push the brake pads onto the disc to slow the wheel down. The discs are often drilled (as shown in the drawing below) so that air will flow through and keep the temperature down.
The picture on the right shows the two brake master cylinders on the Ferrari F1-2000, only visible when the nose cone is removed. These master cylinders contain the brake fluid for both the front and rear brakes. The front and rear systems are connected separately so if one circuit would fail, the driver would still have either the front or rear system with which to slow the car. Also visible is the steering rack and the plumbing for the power steering system.
A newer thing in formula one are the brake ducts. Ferrari introduced these in 2001, with all other teams having it adopted by the end of the season. The right picture shows the box on the inside of the wheel, and the smaller air inlet. The brake duct actually contains a large fan, that rotates around the wheel's axis (upright) and at its same speed. It is in a way some kind of a gas turbo for the cooling of the brakes, powered by the rotating wheel. This causes the fan to rotate very quickly at high speeds, and thus sucking air onto the brakes, where without a brake duct, the air is pushed onto it, just guiding the air to the brake. This brake duct allows the air inlet to be way smaller than it used to be, which generated a considerable aerodynamic advantage.
These brakes are extremely expensive as they are made from hi-tech carbon materials (long chain carbon, as in carbon fibre) and they can take up to 5 months to produce a single brake disk. The first stage in making a disc is to heat white polyacrylo nitrile (PAN) fibres until they turn black. This makes them pre-oxidised, and are arranged in layers similar to felt. They are then cut into shape and carbonised to obtain very pure carbon fibres. Next, they undergo two densification heat cycles at around 1000 degrees Celsius. These stages last hundreds of hours, during which a hydrocarbon-rich gas in injected into the oven or furnace. This helps the layers of felt-like material to fuse together and form a solid material. The finished disc is then machined to size ready for installing onto the car.
The main company that makes brakes for F1 cars is Brembo. Carbon discs and pads are more abrasive than steel and dissipate heat better making them advantageous. Steel brakes as used in CART are heavier and have disadvantages in distortion and heat transfer. Metal brake discs weigh about 3 Kg, carbon systems typically 1.4 Kg. Metal brakes are advantageous in some aspects such as 'feel'. The driver can get more feedback from metal brakes than carbon brakes, with the carbon systems often being described like an on-off switch. The coefficient of friction between the pads and the discs can be as much as 0.6 when the brakes are up to temperature. You can often see the brake discs glowing during a race, this is due to the high temperatures in the disc, with the normal operating temperature between 400-800 degrees Celsius.
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