Experimental Characterization of Brake Pads for Formula SAE Racecar

In Spring 2023, we completed a critical project aimed at supporting the Cooper Union Motorsports team by optimizing their braking system. The objective was to evaluate the frictional coefficient of the brake pad compound used on the 2023 Formula SAE (FSAE) racecar. Achieving brake system performance compliance was essential for passing the Brake Test, a stringest safety check required in the FSAE collegiate racing competition. Failing this test disqualifies the team from key dynamic events, making our experimental results critical.

Project Overview

The FSAE racing rules emphasize safety in braking systems. Our project revolved around testing brake pads for friction, thermal behavior, and performance at high temperatures under load. We specifically tested the EBC GPFAX Race-Only brake pads, which are normally used for motorcycles, in the FSAE vehicle’s ISR calipers. These high-performance pads needed to perform reliably, especially during high-stress events like the Endurance Test, which involves repeated heavy braking over a 22 kilometer-long course.

Brake Dynamometer Design

To assess the brake pads, we refurbished an older brake dynamometer. The dynamometer utilized the vehicle’s upright, hub, rotor, caliper, and pads, ensuring a faithful representation of the car’s actual braking system. Our instrumentation setup included:

  • Rotary encoder to measrure angular position and speed
  • K-type thermocouple embedded in the pads to record temperature
  • Ashcroft G2 pressure transducer to monitor hydraulic pressure in the calipers

The dyno was powered by an AC motor connected to a large flywheel, which simulated the rotational inertia of the racecar’s wheels. We connected these sensors to Arduino microcontrollers, which interfaced with laptops running Serial Studio software for real-time data acquisition.

Experimental Method

We ran a series of controlled braking tests at varying pressures (550-624 psi) to analyze friction coefficients, braking efficiency, and thermal effects. In the Endurance Test, we simulated repeated braking events to measure how rising temperatures impacted pad performance.

The procedure involved heating the brake components with a heat gun before each test to assess the pads’ behavior under near-race conditions. We manually applied pressure to the brake lever, maintaining consistent pressure using mechanical stops to limit lever travel. Each test focused on capturing the rotor’s deceleration, the rise in pad temperature, and the system’s hydraulic pressure response.

Results

The Brake Test revealed that the EBC GPFAX pads provided a reliable friction coefficient, with the highest average value reaching 0.59 - closely matching the manufacturer’s 0.6 rating. Initial tests with higher-than-realistic pressures (624 psi) caused the flywheel to slip on its shaft, slightly distorting the results. After adjusting the test procedure, more realistic results showed that the pads met the required friction levels under cold conditions.

The Endurance Test, though hindered by dynamometer limitations, yielded insightful data. At peak, the pads reached a temperature of 91°C, but the system’s motor struggled to sustain high RPMs for long periods, which prevented full-scale endurance simulation. Despite these challenges, our results demonstrated the pads’ stability in low-pressure, repeated braking conditions.

Conclusions

This project confirmed that the selected brake pad compound had sufficient friction to pass the Brake Test. However, the results also indicated that while the brake pads performed well, the team’s failure in previous years may stem from other issues within the brake system design, such as brake balance or system inefficiences. Future work should focus on refining the braking system, possibly incorporating CAN bus systems for streamlined data acquisition.

Additionally, we recommend further tests with preheated pads to explore brake fade under extreme conditions. This, combined with a more robust dynamometer setup, would allow the Motorsports team to better prepare for race-day conditions.