The size of the discs depends on the circuit and its braking requirements.
Think about racing round one of the World Champion circuits at top speed. Sooner or later, the track conditions will require you to brake. The problem is, you’re going so fast that the force you need to slow down is nothing short of colossal. Well, that’s just the type of force that MotoGP brakes have to offer with about 590 horsepower, more than double that of the engine.
During competition, the most important part of the bike is the front end; almost all of the braking is done with the front wheel and so the front section is where all the weight falls. Ever since the World Championship began, the brake discs have been one of the most important elements of the mechanics and have been subject to a number of changes over the years. Steel brakes used to be the norm, but today they’re usually only used in rainy conditions. Instead, the Repsol Honda Team has innovative front brakes made of carbon. This lightweight material has an enormous braking capacity, but its lifespan in brake discs is usually much shorter than steel, only about 1000 km. The carbon discs of the RC213V are supplied by Brembo, a company with extensive experience in the World Championship.
To ensure it works correctly, the braking system has to be kept at a high temperature, between 200 and 800 °C. This requirement means that these elements are only used for competitions; in normal conditions, they wouldn’t reach those temperatures. During a race, it’s essential that riders warm up the brakes to ensure they will be working properly so they can take the turns with more stability and confidence. The brakes’ temperature increases during the WarmUp Lap, and also during the race.
The size of the discs depends on the circuit and its braking requirements. The most common type are 320 mm, which have a net weight of 850 g. Extremely high temperatures above 800 °C can cause serious damage to carbon brakes, so in highly demanding circuits, discs with a higher mass are used. The higher mass brake discs have more surface area, bringing their weight up to 1000 g, and more of the disc comes into contact with the break pad.
There are also 340-mm brake discs, but the regulations only require them on the Motegi circuit. Thanks to their large diameter, the 340-mm discs generate up to 100 °C less heat because less force is need to brake. There’s also a higher mass version of these discs, which weigh 1200 g.
On the calendar, we can find the three highly demanding circuits according to Brembo, in addition to Motegi, which was already mentioned. Sepang, Circuit de Barcelona-Catalunya, and Red Bull Ring all have areas that necessitate intense braking that puts this part of the bike to the test.
The final result is quite impressive when we look at the numbers. Intense braking can bring a MotoGP bike from 320 km/h to less than 100 Km/h in about five seconds. For example, in the braking portion of Mugello’s turn 1, Brembo recorded a case in which braking brought a bike from 355 km/h to 90 km/h in only 5.2 seconds, and in less than 300 m! It’s clear that the brakes are by far the most powerful part of these magnificent machines.