In single-seater track racing competitions, the only external variable is the rain. In the World Rally Championship (WRC), however, drivers and teams face numerous variables that impact, among other things, the characteristics of the braking system. In addition to the extreme variability in braking conditions, factors such as durability, robustness, and ease of maintenance play a significant role in how rally braking systems are designed and built. 

In the WRC, there are events where the track is covered in snow, others where it’s icy, and some that involve crossing bodies of water. The surfaces in WRC are also highly varied, ranging from tarmac to dirt, sand, and gravel. All of these conditions lead to different levels of grip, which in turn affect the performance of the brakes.

Our approach

Just like in Formula 1, each car in the World Rally Championship is equipped with specific brake calipers, customized in collaboration with the car manufacturers. Brembo technicians co-design the braking system with the team engineers to ensure optimal temperature management under all conditions of use. This is achieved through the use of cooling ducts directed at the caliper bridge, particularly around the pistons.

Our approach places great emphasis on the cooling system, identifying design solutions that maximize airflow to the disc and caliper. Air is directed to key areas such as the brake pad backing plate or around the piston zone to enhance heat dissipation and maintain optimal performance.

Calipers

The WRC brake calipers are made from aluminum alloy and combine 32mm and 38mm pistons. They feature a tunnel in the caliper bridge that connects the outer and inner parts of the caliper, which helps improve the cooling capacity.

 

The design of the calipers is carried out using specific software, known as topological optimization, which maximizes both the stiffness and the weight of the caliper by materializing the caliper only where necessary, supported by CFD (Computational Fluid Dynamics) simulations.

Some teams prefer lighter calipers, even though this may result in lower stiffness, while others sacrifice lightness for greater stiffness, aiming for consistent performance throughout the day. However, most teams use two different types of calipers during the season: one for tarmac events, where the brakes are used mainly for intense, sharp braking and high torque is required, and one for gravel events.

 

Generally, WRC brake calipers work efficiently up to temperatures of 180°C (measured using a thermocouple embedded in the aluminum and transmitted to telemetry). The "alarm threshold" is triggered between 180°C and 220°C, and temperatures above 220°C can lead to critical issues.

Discs

To achieve strong braking on tarmac, Brembo uses cast-iron brake discs with a 370mm diameter at the front and 355mm at the rear, with thicknesses ranging from 30mm to 32mm. Cast iron is a material known for its excellent durability and doesn’t need to be brought up to high temperatures to offer effective braking performance.

 

Over the years, the size of the discs has increased due to changes in regulations. While engine displacement has been reduced, power output has increased by almost 30%, partly thanks to hybrid technology.

 

On gravel, the lower grip forces drivers to frequently correct their steering, but there are fewer sharp braking moments after high-speed sections. As a result, braking power requirements are not as high as on tarmac, so Brembo’s 300mm cast-iron discs with thinner thicknesses (between 25.4mm and 28mm) are sufficient.

The reduction in unsprung mass provided by these lightweight discs improves vehicle dynamics, which is crucial in rally racing, both for acceleration and for rapid direction changes. However, the lighter weight of these discs, due to the reduced amount of cast iron used, could lead to overheating if Brembo had not redesigned the ventilation system to enhance airflow and keep temperatures under control.

 

Depending on the event, teams can choose from different disc thicknesses. For example, in Finland or on the ice in Monte Carlo, brake demands are typically lower, while events in Croatia and Japan place much greater stress on the brakes, requiring thicker discs. The optimal temperature range for the discs is between 450°C and 550°C. Temperatures exceeding 600°C and approaching 700°C can lead to critical issues.

Pads

Even the brake pads for the WRC, which are usually ceramic-based, differ depending on the type of track to be faced. Generally, the compound used for gravel is softer compared to the one for tarmac, in order to avoid wheel lockup and reduce overheating of the discs.

From the blistering heat of Mexico to the icy roads of Sweden, Brembo’s legacy in the World Rally Championship (WRC) is built on resilience and precision.

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Since its debut, Brembo has provided braking systems capable of withstanding the toughest rally conditions.

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As the 2024 season begins, Brembo’s advanced technology continues to support top teams like Ford M-Sport and Hyundai Motorsport, solidifying its place at the heart of the sport.