Design and Manufacturing Process of Optimized Bicycle Crank

Race Face Performance products is a leading designer and manufacturer of performance cycling products. Based in Vancouver, B.C. Canada, Race Face has distribution in over 40 different countries. It specializes in performance cycling components, clothing, and protection. It has been in business for over 20 years.

When planning its next generation bicycle crank, Race Face set out to increase the stiffness of the current version crank arm, without adding any weight. The new crank also had to maintain strength targets. “Our constraints were to manufacture in a cost effective way that minimized tooling cost and processing of each part,” noted Race Face Senior Design Engineer, Chris Heynen.

Traditionally when designing new crank arms, Race Face attempted to maximize stiffness using an I-beam cross sectional design. Attempts were made to optimize the crank arm at the moment of inertial at various sections. From there, Race Face would run a finite element analysis, make changes and recheck until stresses were minimized for the desired shape and weight.

Inspire in the Design Process

After discovering Inspire, Race Face realized that it could greatly enhance and speed up this design process by better understanding material placement within its designs. Race Face also quickly recognized that Inspire’s built in manufacturing constraints would help it to design for its 2D forging process.

To begin concept generation for the crank arm, Race Face first imported a very rough design space into Inspire and applied the materials and loading conditions, as well as a split draw manufacturing constraint. The concept generated in Inspire was significantly different than the I-beam architecture that Race Face had traditionally used.

“From these results I concluded that it was ok to minimize the area around the crank boss,” noted Chris, “so I refined the design space of my model before future optimization, removing all material not essential to the known end design. This decreased the overall starting design space.”

Race Face then used this updated design space to generate concepts for both maximum stiffness and minimum mass.

Chris then imported the concepts into his CAD program and used them to build a final design. Chris noted, “once completed, we created forging tooling based around the Inspire led design. The final creation is a crank arm that is 25-50% stiffer (depending on the test) at the same weight as the previous generation crank arm and much stronger. The increase in the yield strength is directly related to the increase in stiffness.”