Bicycle Brake Caliper Design

Objective: Designed a lightweight bicycle brake caliper optimized for performance and manufacturability.

Requirements: Create a structurally sound, low-mass caliper that met ISO 4210-2 and ISO 4210-4 braking standards. The design needed to minimize material use while withstanding dynamic braking forces and satisfying stiffness, safety, and geometric constraints. Should allow braking distance of less than 10m at cruising speed.

Top Skills: mechanical design (Siemens NX CAD), structural analysis (NX FEA, topology optimization), material selection (ANSYS Granta EduPack), design validation, technical documentation 

Overview

We designed a lightweight bicycle brake caliper to meet ISO 4210 braking standards while minimizing mass and material use. Using Siemens NX for CAD and FEA, we combined Castigliano-based hand calculations, topology optimization, and material selection with ANSYS Granta EduPack. Prototypes were 3D printed in Nylon-12 and tested under realistic conditions. Iterative design refinements, including tapered geometries and truss-like structures, led to a final caliper that successfully stopped a cruising bicycle (~ 20 mph) within 6 meters, well below the 10-meter requirement.

Initial Design and FEA

On top of the project guidelines, the calipers must not interfere with other components on the bicycle. Thus, each caliper must have maximum size constraints, displayed below. These pictures also highlight the load concentration paths when applying boundary conditions and forces.

We performed Castigliano's method hand calculations with specific force and deflection values to predict cable-pull displacements and calculate the ideal combination of caliper thickness values. These calculations were focused on the inner filets near the pivot pins and the mid-span of each arm where the bending moments are largest. This help guide us through our initial design iteration.

From our calculations and assumptions, we applied a 200N tension force where the brake cable pulls the calipers in and a 140N friction force to mimic the brake pad against the tires. 

FEA showed the stresses near the cable attachment points to be too high. We also performed a topology optimization on both calipers. While the results presented would not actually be used due to manufacturing constraints, it gave us a better idea as to where we should improve in our second design iterations.

The updated designs aimed to minimize as much material as possible, tapering in regions FEA showed to have little relative stress. Additional FEA was conducted on the updated designs, showing some improvement in strength against braking forces.

The second iteration designs were also printed out of Nylon-12 through SLS. These were tested on May 19, 2025. Unfortunately, we had minimized the weight too much and failed to provide a strong enough braking force to stop a cruising bicycle within 10m. Furthermore, printed calipers came out rather brittle, so they were easy to snap when holding.

Our previous design showed weakness at sharp changes in geometry, so we decided to go for a truss-like structure of for the left caliper and thicken our right caliper.

Key Takeaways

During final testing, our brake calipers were successful in stopping a cruising bicycle at about 6m, well within the maximum allowed distance of 10m.

One of the biggest takeaways from this is being able to visualize and test our designs within working models of our environment. While we were ultimately successful, we could have been more efficient if we had made an assembly with our initial caliper design within a bicycle. It would have been immediately evident how relatively small and thin they looked, thus allowing us to change it and give them more strength.