Marc Márquez’s crash in the Grand Prix of the Americas at the Circuit of the Americas looked at first glance to be an overly ambitious miscalculation. However, the team’s later explanation gave a little more insight into what happened. Márquez had an issue with the front brake of his Ducati GP23. At the point where he braked hard for the very slow Turn 11, Márquez had almost nothing at the front lever. Grabbing it quickly again, he locked the front wheel and down he went.
The most common cause of this type of crash is “pad knockback.” It happens when the bike hits a bump in the track, the front end wiggles hard, and the pads get jogged back a little from the rotors. Despite the brakes on a MotoGP bike being incredibly exotic, this can—and does—happen to any hydraulic disc brake system, from any manufacturer, whether the rotors are steel or carbon. It even happens with automobiles.
Essentially, braking systems turn the kinetic energy of the moving machine into heat. That heat has to be dissipated as quickly as possible to keep the brake within its operating temperature and working.
Most commonly, motorcycle brake rotors are made of steel. However, in the extreme environment of MotoGP racing, steel simply cannot cool down quickly enough. So, carbon rotors are used. Steel rotors would need to be ridiculously large—around three times the size—to achieve the same level of braking performance as carbon.
The carbon rotors are gripped by carbon pads within the Brembo GP4 caliper. Each rotor is made from layered carbon material that is baked in an autoclave under enormous heat and pressure. Each disc takes approximately nine months to make—hence the mind-bending cost of around $10,000 a pop. Brembo supplies all the MotoGP teams.
The carbon rotors start working well around 250 degrees C, and the performance drops off at around 900 Degrees C. In typical operation, the goal of the Brembo engineers is to keep the disc temperature at around 500 degrees C. However, the challenge is heat build-up, as track layouts are so different.
For example, Mugello Circuit has an incredibly high-speed straight followed by a slow corner, with the following corners flowing nicely with no hard braking areas. This allows the brakes plenty of time to cool down.
Conversely, Mobility Resort Motegi has several—albeit slower speed—hard braking points one after another, so although the brakes do cool somewhat in between, they never get the chance to cool completely, and the heat keeps building. That kind of environment poses the biggest challenge for Brembo’s engineers.
Brembo’s answer is supplying three diameters of carbon rotors—320, 340, and 355mm—with the larger two being available with larger surface area High Mass options, making five geometries in total. These are available in different specifications—Standard, High Mass (with the larger braking surface requiring larger carbon pads), and Finned rotors for situations needing extreme cooling. The rotors all have the same thickness (8mm), and the same Brembo GP4 caliper is used by all the teams on the rotors of all specifications.
During the season, most teams focus on the 340mm discs, alternating between High Mass (larger braking surface) and Standard Mass (smaller braking surface) at different circuits and according to rider preference. The largest 355mm rotors are typically used on heavy-braking circuits such as The Red Bull Ring, Buddh International Circuit, Chang International Circuit, Sepang International Circuit, and Motegi. The weight of each rotor varies between 1 and 1.4kg, depending on the size and specification used.
Carbon pads are employed, and made from exactly the same material as the rotors. Once a set of pads is used on a rotor, they wear in unison and become matched, making it vital that the same pads are always used on the same rotor. The pair can be interchanged between wheels, but the used pads and rotors must remain together. If necessary, the rotors can be re-machined to take them back to as-new condition, and a new pair of pads can be used to start the process again.
The problem for the rider is that the bigger and heavier the rotors are, the harder it is to turn the bike. Naturally, the riders want the rotors to be as small as possible to keep the bike agile, while Brembo wants to use rotors as large as possible to achieve maximum braking force with the least stress on the system.
Brembo’s R&D effort focuses on making the rotors, calipers, and pads as efficient as possible so the rider can use the minimum size without compromising braking performance. Although the choice is primarily left up to the rider, different levels of brake rotor have to be used at various circuits depending on how demanding they are.
Beyond simply using hydraulic pressure from the lever, amplification of the braking force is created by machining the calipers and pads so that they are slightly wedge-shaped. As the rotors turn forward and the pads start to grip the rotor, the pads are allowed to move slightly forward—around a millimeter or so. The wedge shaping mechanically increases the pads’ grip slightly by forcing the pads into the rotors—a bit like a wedge door stop. This also helps rider feel at the lever. The tolerances are extraordinarily precise, so the machining costs make the brake system more expensive. Amplification is only used in MotoGP, and not in Moto2 or Moto3.
All the teams in MotoGP use the Brembo brake system, and each Brembo GP4 caliper is machined from a single piece of billet aluminum. This one-piece construction ensures the unit expands and contracts as one piece, maintaining consistency even when the temperature reaches 900 degrees C. Multiple external fins across the caliper help with cooling.
Marchesini wheels can have a silver-like coating to help reflect the heat coming off the rotors in an ongoing effort to prevent that heat from reaching the front tire and increasing the air pressure inside the tire. Marchesini Wheels is part of the Brembo Group.
Once the rider releases the brake lever, the pads release their grip on the rotor. This action is helped by spring-loaded pins built into the calipers to help push the pads away from the rotors after the brake is released, ensuring that the pads don’t drag against the rotors. The spring pressure is clearly a resistant force against the rider’s input to the pads via the brake lever, so the spring pressure must be carefully balanced, as too much spring pressure affects brake feel and power.
The four pistons are activated by hydraulic fluid pushing the carbon brake pads against the rotor to achieve the braking effect. A one-way valve inside the caliper prevents the fluid from being pushed back up the lines and reduces the pad knockback effect. Still, as shown by the Márquez crash at COTA, it’s impossible to completely prevent it.
When you watch the Spanish GP this weekend, keep in mind that while the brakes on a MotoGP bike don’t look entirely different from what is on your motorcycle, there is an astonishing amount of Brembo technology built into the MotoGP binders.
Photography by Arthur Coldwells
