Standard tube selection for recumbent bicycle frame using simulated finite element analysis

The number of bicycle users are increasing significantly, however many of bicycle designs are not suitable with urban condition. Generally, the urban road is smooth and flat, but there are many junction and trafic, so that a city bicycle should be specifically designed for that condition. Department of Industrial Engineering has conducted a research focused on the ergonomics city bicycle. The result of research is the recumbent bicycle using Short Wheel Base (SWB) was selected as the best concepts instead of upright bicycle. The research has continued to develop its compatibility with standard bicycle components to improve its manufacturability and maintainability which eventually resulted a first bicycle prototype. We keep steel as its frame material because it has low price, high manufacture ability, high formability more than other materials that highly recomended for city bicycle. Unfortunately, the frame weight of the prototype is still 50% heavier than the upright bicycle with the same steel frame material because the weight or frame tube geometry was not concerned in the previous researches. Basically, heavier frame cause higher energy consumption during riding and makes the rider more easily tired. Different from upright, a SWB recumbent bicycle has single main frame construction so that it needs thicker material for maintaining its strength and stiffness, but it is still necessary to find the best tube geometry which can provide both lightness and strength. This study aims to select 44.5 mm outer diameter 1020 DOM A513 standard round steel tube size for SWB recumbent bicycle frame material. This research uses simulated Finite Element Analysis (FEA) method with Autodesk Inventor to determine stifness and weight of each steel tube alternatives. As the result, the steel tube with wall thickness of 2.8 mm is selected to be the best material for SWB Recumbent Bicycle.