Here's why carbon is unavoidable for the discs and brake pads in the top competitions

11/21/2018

In Formula 1, the carbon brakes have been used ever since the ‘80s and today most of the top motorsport competitions make use of this friction material both for discs and brake pads.

As you have surely guessed, we are dealing with the Holy Grail of brake materials. In fact, no other element offers carbon's same combination of light weight, high thermal conductivity and absence of thermal expansion.

These characteristics result in a high coefficient of friction, in stable and consistent performance and in an almost instantaneous heat dissipation. In order to know this element better, here are 5 curiosities about how it is used.

CARBON IS NOT EXCLUSIVE TO FORMULA 1

The incredible braking power of the modern Formula 1 single-seaters – from 300 km/h to 0 in less than 3 seconds– can not be set apart from the use of carbon discs and pads.

However, carbon brakes are not exclusive to Formula 1, but have been used for decades on the prototypes that compete at the 24 Hours of Le Mans and in other WEC (World Endurance Championship) races.

However, to make the most of carbon in endurance races the main problem for this kind of application has to be overcome, wear! The friction material must withstand 24 hours of continuous use, against a maximum of 2 hours for the F1 Grand Prix races.

A real challenge for Brembo, which has developed specific solutions to best fit heavier cars in a context that is not just related to pure performance: The discs' diameter is different, because in this case 380 mm diameters can be the reached with the 18” rims, but the thickness is anyhow 32 mm.

The main developments of the last few years have mainly focused on reducing fuel consumption and this has lead to the development of low wear materials.

For a 24 hour race, avoiding to replace worn out discs and pads during race saves valuable time and can be “decisive” for its outcome. A new friction material that greatly increased the mileage and guaranteed a more effective thermal conductivity was introduced by Brembo already in 2001. It allowed the Audi R8 of the Joest Team driven by Frank Biela, Emanuele Pirro and Tom Kristensen to end the race in first position, without having to replace the discs and pads not even once.

In recent years, the incredibly low wear has allowed to keep the performances unchanged and repeatable from the beginning to the end of the race.

Also Formula E relies on carbon. In fact, starting from its fifth season (2018/19), Brembo will be the exclusive manufacturer for this category's braking systems.

In order to better meet the requirements of an all electric car, the carbon that is being used is different from the one that is used for the Formula 1 and for the WEC. Furthermore, Formula E's carbon discs' thickness is significantly less: 24 mm in the front, 20 mm at the rear.

Formula 1 vs Le Mans: a comparison of Brembo braking systems
The differences and similarities in brakes on an LMP1 car and a Formula 1 car. Brembo compares the braking systems supplied to the teams of the two competitions.

CARBON IS ALSO USED ON BIKES

In addition to the major car racing categories, carbon discs are also used in the motorcycle World Championship but only for the MotoGP.

This material had made its tentative top class debut in 1988 and within five years it had become the absolute standard. Too great the difference in performance, as well as that in weight (the brakes are unsprung weights) and in feeling, when compared with the steel discs that were previously used.

Now most MotoGP riders prefer 340 mm discs, split between High Mass (wide surface) and Standard (narrow surface).

In order to ensure the same braking torque and obtain a further lightening, Brembo has also introduced the 340 mm diameter Light discs.

Other riders instead will continue to use the 320 mm diameter discs. Furthermore, two different carbon compounds are available for each size of brake disc and pad. They differ for the initial bite and for their resistance to high temperatures.

In an application where the feeling during braking is crucial for the rider, Brembo offers an overall choice of as many as 10 different brake disc options. The absence of carbon discs in the Moto2 and Moto3 is instead due to cost-saving reasons.

A similar reason is at the root of carbon being excluded from the Superbike World Championship since 1994: stainless steel discs are used for this latter championship and most of them are made by Brembo.

BREMBO BRAKES FOR THE 2018 MOTOGP WORLD CHAMPIONSHIP: ALL THE TRENDS.
Brembo brakes for all the MotoGP riders for the 2018 season too, but each rider with a personalized approach.

CARBON: THE HIGH CONDUCTIVITY PUSHES VENTILATION

One of the most critical aspects for the braking systems on Formula One's single-seaters has always been handling the operating temperatures. To better meet the heat dissipation requirements, the ventilation of Brembo's carbon discs has undergone a constant evolution.

In 2005, each disc had a hundred or so ventilation holes while now, due to the progressive reduction in size, there are more than 1,400 of them. The holes in Brembo's carbon discs currently measure 2.5 mm in diameter, they are arranged in 4 or 5 rows and are manufactured with a machining tolerance of just 4 hundredths of a millimetre.

The holes' shape and number are related to the characteristics of the single-seater on which the disc will be used. In fact, CFD (Computational Fluid Dynamics) is used for developing the ventilation according to each car's characteristics.

For the LMP1 hybrid prototypes, where the regenerative braking is greater than in Formula 1, the ventilation holes are fewer. When braking in Formula 1 the discs' temperature can actually reach peaks of over 1,000 degrees centigrade. Instead at the 24 Hours of Le Mans the problem is often the opposite because at night or during the neutralisation phases the risk is that the systems' temperature may fall below 300 degrees Celsius.

This is the limit under which the friction material can suffer from the dreaded glazing effect. As for Formula E the maximum temperatures are around 800 degrees Celsius, Brembo's carbon discs presently just have 70 ventilation holes with a 6.2 mm diameter on the front discs and 90 holes with a 4.2 mm diameter on the rear discs.

CARBON ALSO WORKS ON WET SURFACES

Since carbon discs have started to be permanently used in Formula 1 the drivers have no longer been able to do without them, not even in case of rain.

The reduced grip due to the wet asphalt and the direct contact with the water which increases the heat exchange cause a drop in temperature. But despite this and thanks to the enormous braking power these single-seater have, the drivers just need a few braking sections during the warm-up lap to reach the ideal operating temperature, this with only a slight air intake partialisation. But for motorcycling the situation is different, the brake discs run in free air and cool down much more quickly.

Also the fact that the wheels are only 2 prevents all the braking force produced by Brembo's carbon system from being transferred to the ground.

Not by chance no later than a year and a half ago steel discs were preferred to carbon discs when it was raining. This because the latter could not ensure a good coefficient of friction, as they could not reach the minimum operating temperature, that is set at 250 degrees Celsius. However, Brembo has never stopped improving its materials' manufacturing processes.

So, thanks to the bikes' increased power, to the more performing tyres and to the use of covers for the discs, it has succeeded in the impossible challenge: in 2017, at the Japanese GP, despite the rain that didn't give the riders any respite for all the 24 laps and that made the asphalt's temperature drop to just 15 degrees centigrade, the first 9 riders that made it to at the finish line had used carbon discs.

Brembo behind the first MotoGP triumph with carbon discs in the rain
They said it was impossible, but that didn't stop Brembo.

ON THE ROAD CARBON-CERAMIC IS BETTER

Although, when driving on a track, the carbon discs ensure the substantial benefits listed above, they are not suitable to be used on the road.

They are unsuitable mainly in terms of performance because every day driving does not allow the braking system to reach the minimum operating temperatures that carbon requires.

Another factor that excludes them from being used on road going cars is the high consumption: during the 24 Hours of Le Mans, a prototype's carbon disc looses 3-4 mm of its thickness and a pad 8-10 mm.

Even if a lower consumption is acknowledged for road supercars, the duration would anyhow be too low to justify the expense. Indeed, because another limit of the carbon discs is definitively their high cost, as their exclusion from many not top-level car and bike championships shows.

In order to bring, at least in part, most of the many advantages that carbon can offer, also to the road going cars, Brembo has created the carbon-ceramic discs. This thanks to Brembo SGL Carbon Ceramic Brakes joint venture with the SGL Group, which is the world's main producer.

The carbon-ceramic discs offer a 5-6 kg weight saving when compared to a traditional cast iron disc. They can last, depending on the driving style, as long as the life of the vehicle on which they are fitted, as well as reducing the braking distance from 100 km/h to 0 km/h of about 3 meters.

Furthermore, Brembo's carbon-ceramic discs, resit to corrosion, they do not warp with temperature, they do not vibrate, they are reliable even when it rains and they provide the same braking force even after repeated operation and at low temperatures.

Carbon-ceramic discs: High performance, minimum weight