Formula 1 braking systems have been in the spotlight during the 2014 F1 season, not least due to a number of crash inducing failures notably that of Kamui Kobayashi at the Australian Grand Prix and Lewis Hamilton at the German Grand Prix.

Kobayashi’s brake failure was in fact a brake by wire (BBW) system failure – that system is detailed in a separate article which can be read here: What is brake by wire?

On the other hand Hamilton’s failure was caused by a failure of the traditional braking system which is what is detailed in this article.

This page: Friction materials (discs & pads) –

Part 2: Calipers

Part 3: Cooling

Part 4: Statistics

PART 1: Friction material

The brakes on a Formula 1 car may look hugely complex but in reality they work in the exact same way as the ones on your road car do. When the driver presses his brake pedal he is pushing hydraulic fluid down lines to push out pistons in the caliper (sometimes called ‘pots’ – i.e. six pot calliper). These pistons push pads of a special friction material into the rotating disc which is linked directly to the wheel.

“Formula One cars, in common with military aircraft and a few of the more modern passenger aircraft, use a brake material that is significantly different to what we find on road cars” Williams F1’s Pat Symonds explains. “A typical road car uses a cast iron brake disc with an organic brake pad. In an F1 car, though, the same material is used for both disc and pad, and this material is known as carbon-carbon – a significantly different material to the carbon-fibre composites used in the rest of the car. Carbon-carbon is essentially a pure form of carbon and is both extremely light (approx. 50% of the weight of standard materials) and also possesses a higher coefficient of friction at the correct operating temperatures. This peaks at around 0.6, compared to 0.3 for conventional materials.”

In 2014 three companies supply carbon friction materials Hitco, Safran (Carbon Industrie) and Brembo. It may not seem obvious at first but the new power units have a significant impact on the design and operation of the brakes on all of the cars, and not just with BBW.

The minimum weight of the cars has been increased to 691kg, which will obviously mean that the brakes especially at the front may have a harder life. “For 2014, a greater proportion of braking force will be transferred to the front axle with the maximum brake torque ideally decreasing due to the reduction of downforce and speed of the cars. Stopping distance, on the contrary, will be greater and, consequently, time spent under braking increasing” Brembo’s 2014 season notes explain.

In addition at the rear the energy recovery system (ERS) does a notable amount of braking work when it is harvesting. So for these reasons the rear brake discs can be smaller in diameter compared to 2013, with a resulting advantage in terms of weight and speed of response to pressure. Their thickness may also be thinner (25mm).

Due to these changes in demand all three suppliers have introduced new brake materials onto the grid in 2014. Brembo calls its new materials ‘CER’ which it says “considerably reduces wear, guaranteeing more effective thermal conductivity. Compared to previous material, CER offers excellent warm-up time; that is, maximum rapidity in reaching more efficient operating temperatures; a wide application range in terms of both pressure and temperature, and very smooth friction performance. All these features provide the driver with a perfect modulation of the braking system. The incredibly low wear results in more reliable performance from the start to the end of race. Disc material is the same for all teams supplied by Brembo, who continues to research and develop composite materials that are more manageable” again from the Brembo preseason notes.

It was revealed when the Brembo discs failed at Hockenheim that Brembo has more than one product for F1 teams on offer, some even suggest that Ferrari is using discs made from the older ‘CCR’ material. The specific material and combination of brake suppliers and materials used on a Formula 1 car is very driver specific, different drivers tend to want different things. At Hockenheim both Mercedes drivers tried different combinations of brake materials and suppliers in Free Practice, Brembo and Safran. In the end Rosberg opted for the CI brakes on the front and Brembos on the rear while Hamilton opted for Brembos all round.

“When we assess brake performance, we do so largely in terms of two parameters: bite and consistency. Bite is the initial friction experienced when the driver first presses the brake pedal and the brakes are not yet at the correct operating temperature. Consistency is a measure of how consistent the friction is for the duration of the braking period” Symonds adds. “Carbon-carbon brakes possess very particular properties. A carbon brake has relatively poor performance below about 400°C and has optimum braking performance above 650°C. Unfortunately, whereas conventional brakes wear down through the normal mechanism of wear that any frictional material experiences, a carbon brake not only suffers wear through this mechanism but also a process called oxidisation. Oxidisation is in simple terms a burning of the surface of the disc, and at temperatures above 600°C it is accelerated and becomes the main mechanism of wear. Bearing in mind that during a braking event the temperatures of the brake discs will reach around 1200°C, it can be seen that oxidisation is extremely significant in the brake wear process. On the straights of course, the brake ducts are feeding air to the brakes and so they drop below the oxidisation temperature but as they still maintain these high temperatures for a relatively long time, paradoxically the very air that is being used to cool them contains a high amount of oxygen that accelerates the wear process.”

When a carbon brake disc wears out or overheats it can fail in a spectacular way, with a sudden and instant explosion. This is what pitched Hamilton off the track in Germany. The video above, taken during filming for a television series, shows what can happen when a disc fails.

PART 2: CALIPERS – ALL ABOUT STIFFNESS AND WEIGHT

