Performing Finite Element Analysis (FEA) on bicycle frames has become a common activity for bicycle designers and engineers in the hope of improving the performance of frames. This is typically achieved by balancing priorities for key requirements, including minimising the mass of the frame (possibly using competition rules to constrain this), maximising lateral stiffness in the load transfer from the hands and feet to the drive, maximising the strength capabilities of the frame to allow for a higher load capacity or better load distribution, and adjusting the vertical compliance of the frame to tune the softness of the ride. FEA has been used to analyse composite, aluminium and steel bicycle frames with the aim of understanding physical behaviour and improving performance relating, however a comprehensive study on the influence of key geometric parameters on the stiffness of frames has not been conducted.
I’ve recently undertaken a project to evaluate the influence of key geometric parameters on frame stiffness using a wide range of bicycle frame designs from historical data and to compare these to an optimised solution. I’ve created a model that simulates two standard loading conditions to quantify the vertical compliance (a sample displacement plot shown here) and lateral stiffness characteristics of 82 existing bicycle frames from the bicycle geometry project and compares these characteristics to an optimised solution in these conditions. Perhaps unsurprisingly smaller frames (490mm seat tube) behave the most favourably in terms of both vertical compliance and lateral stiffness, while the shorter top tube length (525mm) and larger head tube angle (74.5°) results in a laterally stiffer frame which corresponds with findings from literature. The optimised values show a considerable improvement over the best of the existing frames, with a 13% increase in vertical displacement and 15% decrease in lateral displacement when compared to the best of the analysed frames. The model has been developed to allow for further develop to include more detailed tube geometry, further analysis of more frame geometries, alternative materials, and analysis of other structural characteristics. The full details of this work will be presented at the International Sports Engineering conference in Sheffield in July 2014. I’ve also started working on the next phase of this, expanding the range of frames, and including more detailed tubing geometry…watch this space!