The ultra-light material behind a remarkable F1 attribute

Whenever a group of car enthusiasts gather to talk about performance it’s not long before acceleration numbers are bandied about.
 Very rarely does braking performance get the bragging rights. In absolute terms a Formula 1 car’s acceleration is impressive but not necessarily outstanding, since some hypercars now have power-to-weight ratios approaching that of
 an F1 car and tyre grip becomes a limiting
 factor. When it comes to braking, however,
 it’s a very different story.

One of the best-performing road cars, the Bugatti Veyron, can brake at around 1.3g. In this context ‘g’ is a measure of deceleration and is equivalent to losing about 22mph every second. An F1 car’s peak braking deceleration is around 5g, meaning it could lose that 22mph in a tenth of a second.

The amazing performance of the F1 car is down to the type of brakes used and the immense downforce and, hence, grip that it has. Of course the magnitude of the downforce isn’t constant
 and diminishes with speed. This means that
 while the peak braking may be nearly 5g the average deceleration during braking is more
 like 3g – still an impressive figure.

If we consider a hard braking event – I’ve chosen braking for Turn 7 in Singapore – we can examine data to see how remarkable the brakes on an F1 car are. On his way to pole in 2022 Charles Leclerc approached the corner at around 180mph. He hit the brakes, probably exerting around 1600 Newtons, or 360 lbs in British units, of force on
 the pedal. Leclerc then came off the brakes to enter the corner at just over 75mph two seconds later.
 His total braking distance was less than 100 metres. Think of that (but don’t try it!) next
 time you approach the 100-metre board before a roundabout at 70mph on a dual carriageway.

Since there’s no anti-lock braking system on a Formula 1 car, the driver needs to modulate the brake pressure by releasing the brake progressively as the speed, and the downforce with it, decreases.
 This is a very particular skill needed on racing cars and isn’t easy
 to acquire. Get it wrong and a wheel will lock, possibly causing severe damage to the tyre.

To make things even more difficult, the braking friction is lower at the start of braking, when the disc and pad are cooler, than at the end of braking when the brakes have got hot.
 Of course these are relative terms and the disc will probably he
at around 400 degrees at the start of
 braking, rising to up to 1200 degrees, the temperature of molten lava, by the time 
the driver comes off the pedal. 

When an F1 car jams on the anchors, the physics involved are mightily impressive

Photo by: Zak Mauger / Motorsport Images

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 hits the brake pedal and the brakes aren’t yet at the correct operating temperature. Consistency is a measure of how consistent the friction is for the duration of the braking period.

To get this consistency with the enormous duty cycle experienced, F1 cars, in common with military aircraft and some more modern passenger aircraft, use a brake material significantly different from what we find on road cars.

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 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 (approximately 50% of the weight of standard materials) and possesses a higher coefficient of friction
 at the correct operating temperatures.
 This peaks at around 0.6, compared with
0.3 for conventional materials.

The brake ducts themselves are highly complex and different configurations are required depending on the braking severity of the circuit

Manufacturing carbon-carbon discs is a lengthy process which takes hundreds of hours. The complexity of the procedure also explains the other major property of carbon-carbon brake discs and pads: cost. A complete car set of brake discs and pads costs around £15,000, and the team will probably use 50 sets in
 a year. The brake callipers don’t come cheaply either: a complete
 car set costs a further £15,000.

Apart from cost, one of the reasons carbon brakes aren’t used on road cars is that they wear extremely quickly. To be more exact, 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 abrasive 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. This means that when the brakes are giving best performance they’re also losing mass rapidly through oxidisation which occurs not just on the rubbing surfaces.

Carbon-carbon brakes are designed to work in very specific conditions which improve performance at a cost of durability

Photo by: Motorsport Images

On the straights, of course, the ducts are feeding air to the brakes and so they drop below the oxidisation temperature. Paradoxically the very air used to cool them contains a high amount of oxygen that accelerates the oxidisation process.

The brake ducts themselves are highly complex and different configurations are required depending on the braking severity of the circuit. Teams will always use the smallest duct possible since large ducts harm the aerodynamic efficiency. The air is fed both through the multiple 3mm diameter radial holes drilled in the discs and 
across the surface of the disc and pads. The hot
 air exiting the brakes also has an effect on tyre heating, less so since the introduction of the
 2022 regulations, but still a factor.

While not grabbing the headlines that power units get, the brakes on a Formula 1 car are equally important to a good lap time.

Effective braking performance remains crucial to good laptimes

Photo by: Zak Mauger / Motorsport Images