MotoGP remains a prototype racing series, despite the increasing use of spec components. In 2009, MotoGP switched to a single tire supplier, a spec ECU in 2014, and spec software in 2016. Bore and stroke, and the number of cylinders are specified, meaning that all six manufacturers in MotoGP use four-cylinder 1000cc engines with an 81mm bore.
Despite the fact that so much of the rest of the bike design is unregulated, some components become almost de facto spec. The choice of brake component suppliers is completely free, and yet every MotoGP bike on the grid is fitted with parts that come exclusively from Brembo, the Italian brake manufacturer which dominates the sport, on both two wheels and four.
At Brno, I had the chance to talk to two people with intimate knowledge of Brembo's braking components: Andrea Pellegrini, chief engineer for Brembo inside the MotoGP paddock, and Santi Hernandez, crew chief for world champion Marc Márquez in the Repsol Honda team. Pellegrini provided the perspective from the side of the brake manufacturer, while Hernandez gave an insight from the end users' point of view.
New tires, different braking styles
Pellegrini first gave an insight into how the brakes have changed over the years, and the factors which drove those changes. "For example, when they moved from Bridgestone to Michelin, the brakes also were affected by this change," the Brembo engineer said. "Also with Michelin in the last few years, the performance of the bike has increased, so also the energy going into the brakes is higher compared to two or three years ago."
At heart, that is what the brakes are: a method of converting motion back into energy, reversing the process of the engine, which takes energy and converts it into motion. As the bikes have improved, and engines got faster, the brakes have had to absorb more energy to slow the bikes down. "We saw this trend, collecting the data from all the teams, coming from the bike, the setting of the bike, also the engine of the bike. Also the laptime is going down every year, so they put more energy into the brakes," Pellegrini explained.
Since their return to MotoGP, Michelin have made big steps forward, improving their tires to the point they are generating more grip, and as a consequence, smashing pole, lap, and race time records. But the change from Bridgestone to Michelin also meant changes to the way that riders had to use the brakes to deal with the available grip.
Grip, energy, and braking
"I think how the riders apply the brakes is more different," Pellegrini said. "Because you have to put energy into the brakes, but the grip you have between the asphalt and the bike, that depends on the tire. So the more grip you have, the more energy you have in the brakes." The stiffer carcass of the front Bridgestone made a difference as well. "Also because of the structure of the tire, how the rider is pushing on the brakes is different."
Though the switch to Michelins changed the way riders braked, the difference was not enough to require a complete redesign. "The carbon discs are exactly the same," Pellegrini explained. "We developed different solutions in the caliper, different solutions on the pads and the discs."
In terms of brake discs, the fundamentals are the same: there are two different sizes of carbon discs, 320mm and 340mm, and both sizes are available in high mass and standard mass. The high mass discs are exactly that: thicker and heavier, they carry more material, in order to absorb and disperse the energy demanded by braking. At a track like Motegi, the demands on the brakes are enormous, which is why the FIM mandated the use of the larger 340mm discs.
At a track like Phillip Island, where riders use the brakes much less, a smaller disc with standard mass is enough to cope. In Australia, the weather conditions can also play a part, the cold and the wind rapidly sucking heat out of both tires and brakes. Being able to get heat into the brakes quickly is more important there, to ensure maximum braking performance.
Maintaining the brake discs inside their working temperature range is the primary objective of the crew chief, Santi Hernandez explained. "The only thing you have to care about the brakes is the temperature," the Repsol Honda crew chief said. "To be inside the range Brembo gives to you. Because the carbon discs have to be at least 300°C, but also the maximum you cannot be over 800°C. So you need to be inside that range."
Managing that aspect depends on a whole range of factors, Hernandez explained. "What you need to think about the setup depends on the circuit, how demanding is it of the braking, and also depending on the weather temperature. You have to understand if you have to use the 320mm high mass, 340mm, use the brake covers, full covers, or no covers on the disc. This is for me the most important starting point for the brakes."
"From that point, you have to check especially the minimum and maximum temperature when you check the data. If you are inside the range, and the riders are not complaining, you are not playing so much with brake setup," the Repsol Honda crew chief said.
Heat is the enemy
There are some circuits where this is more of a factor. Motegi is one such place, as Ben Spies demonstrated when he crashed due to his brakes overheating during practice. The Japanese circuit is somewhere you have to be more careful, Hernandez said. "In Motegi, where you have a lot of high peaks of temperature, and also it's a circuit where there are very high demands on the brakes, there you are paying more attention. Because of course, one of the problems there is if you have some trouble, the rider can be in a dangerous situation."
"Because at high temperature, you have oxidation of the carbon material and then you have a lot of wear," Brembo's Andrea Pellegrini adds.
"And also the calipers," Hernandez points out. "If the temperature of the calipers gets very high, the oil seals can leak and you can lose pressure." Pellegrini nods, adding "The lever becomes spongy...."
The danger is not from the temperature spiking, but from a sustained rise to levels beyond the performance window, Hernandez continues. "You can see a peak sometimes, but if it's just one peak, it's not a problem. The problem is that if that peak is at the same point every time, and every time it is longer and longer. That's where you have to pay attention. And also when the weather is not stable, you have to pay attention all the time to which cover you have to use, or which disc you have to use. To keep the brakes always inside the range. Because at the end, the performance of the brakes, especially the carbon brakes, is all down to temperature."
Different riders, different loads
How the brake temperature changes depends a lot on both riding style and bike design. The aim is to have consistent performance, the Repsol Honda crew chief said. "The target of the brakes is for the rider to always have the same feeling, to be in the range where the carbon discs need to work, don't overload them, and don't be under the minimum. And of course you have to pay attention and check how the layout of the circuit is and how you are using the brakes. Especially with your rider."
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