Custom made

Custom lightweight construction – Made in Germany

Many cyclists face the challenge of choosing the right racing frame from manufacturers' pre-defined geometries to best fit their body measurements. Finding the right frame is tricky because standard frames are typically sized in increments of multiple centimetres and are limited in their accommodations for different body proportions. In this case, individual components are selected to adapt the bike to the body. It's not uncommon to see racing bikes with very long or short stems and an additional tower spacer. For this reason the Fraunhofer Process Innovation Project Group at the University of Bayreuth collaborated with ax-lightness GmbH to develop a customizable bike frame made of carbon fibre-reinforced composite, or simply "carbon". The frame, which uses some of the same special materials applied in Formula 1 racing, is one of the world's lightest bike frames suitable for racing. The challenge in developing such a frame was designing and manufacturing each frame specifically for the demands of the rider so that every single one is a unique specimen. A process chain was created to cover every step from the dimensioning of the customer to production with the custom fitted bike as the final product. A specially developed calculation program acts as the interface between the customer's dimensions and the production. Individual tubes and the frame structure as a whole are inspected using simulations and strength analyses.

Custom frame manufacture not only results in superior riding comfort thanks to the rider's optimum sitting position on the bike but also improves power transmission to the pedal. To produce an optimum frame geometry for the rider the Fraunhofer Project Group created an optimized process chain that includes everything from recording body measurements all the way to the final customized bike frame. Working with "bike fitters" like Jürgen Schulz in Neuenmarkt, who offer their expertise in biometric measurement and position analysis on the bike, it is possible to record the customer's anatomical data. This geometric data is then used to create a custom frame geometry. A calculation program was developed to reduce the amount of work and increase the accuracy of the dimensions for production. The program calculates the geometry of the frame based on the sitting position entered and thus represents the input parameters for its production.

Weight, stiffness, comfort and engineering strength are the basis for a successful bike frame. Computer aided stress simulation (Finite Elements Simulation) is an important work step in the optimization of stiffness and frame weight (see figure 2). First, test rides were performed in order to determine the adjacent forces on the frame. We then defined various maximum loading cases based on these test rides in order to subsequently perform the simulation. The simulation allowed us to examine the layer structure of the anisotropic (direction-dependent) material based on shifting and strength criteria in order to ensure the amount and best possible orientation of fibre mats.

Today the frame is manufactured using the "tube to tube" method in which individual tubes are assembled into one frame. In the course of this project we are also developing a way to manufacture the frame in a monocoque design because, compared to other production methods, using continuous fibre mats at the joints improves stiffness while retaining the same weight. By employing a modular moulding concept to manufacture the frame in a monocoque design we believe it is possible to continue to manufacture the frame in Germany in an economic manner.