Abstract—The difficulties in riding small wheel bicycles and their lesser stability have been perceived for a long time. Although small wheel bicycles are designed using the similar approach and guidelines that have worked well for big wheel bicycles, the performance of the big wheelers and the smaller wheelers are markedly different. Since both the big wheelers and small wheelers have same fundamental geometry, most blame the small wheel for this discrepancy in the performance. This paper reviews existing guidelines for bicycle design, especially the front steering geometry for the bicycle, and provides a systematic and quantitative analysis of different wheel sized bicycles. A validated mathematical model has been used as a tool to assess the dynamic performance of the bicycles in term of their self-stability. The results obtained were found to corroborate the subjective perception of cyclists for small wheel bicycles. The current approach for small wheel bicycle design requires higher speed to be self-stable. However, it was found that increasing the headtube angle and selecting a proper trail could improve the dynamic performance of small wheel bicycles. A range of parameters for front steering geometry has been identified for small wheel bicycles that have comparable stability as big wheel bicycles. Interestingly, most of the identified geometries are found to be beyond the ISO recommended range and seem to counter the current approach of small wheel bicycle design. Therefore, it was successfully shown that the guidelines for big wheelers do not translate directly to small wheelers, but careful selection of the front geometry could make small wheel bicycles as stable as big wheel bicycles. Keywords—Big wheel bicycle, design approach, ISO requirements, small wheel bicycle, stability and performance. I. INTRODUCTION ICYCLES share a long history of more than 200 years with us. Since the invention of the bicycle in 1817 by Karl Von Drais, it endured various design modifications before evolving as a relatively safe vehicle “safety bicycle” in 1890 [1]. The safety bicycle had two equal sized pneumatic wheels, drive chain, brake callipers, and closely resembles the modern bicycles. Ever since the evolution of the safety bicycle, a number of frame builders or bicycle manufacturers have been established, and a plethora of bicycle designs have emerged in Milan Paudel is with the Nanyang Technological University, Institute for Sports Research, 50 Nanyang Avenue, 639798 Singapore (corresponding author, phone: +65-81486808, e-mail: milan002@e.ntu.edu.sg). Fook Fah Yap is with the School of Mechanical and Aerospace Engineering, Nanyang Technological University, 50 Nanyang Avenue, 639798 Singapore (e-mail: mffyap@ntu.edu,sg). Anil K. Bastola is with the Nanyang Technological University, Institute for Sports Research, 50 Nanyang Avenue, 639798 Singapore (e-mail: anilkuma001@e.ntu.edu.sg). the market. The other descendants of the bicycle are scooters and motorcycles. The motorcycle design procedures have matured over the time. Various simulation software is radially available to evaluate the performance of the motorcycle during the design procedure. However, bicycle design is still a matter of craftsmanship rather the engineering. Most of the frame builders use trial and error methods or some empirical guidelines derived based on the experiences [2]-[6] to design the bicycle frames. Those guidelines are basically used to maintain the cyclist’s ergonomic in the bicycle. Cyclist’s body parameters such as overall height, torso length, leg inseam length, arm length etc. are taken as the design input. Then, the frame design parameters such as saddle height, handlebar height, saddle to handlebar reach, bottom bracket height reach, stack are selected based on these rider’s anthropomorphic parameters and the derived guidelines. On the other hand, headtube angle and trail are chosen based on the experiences. This bicycle design methodology has remained stagnant for a long time. This is because the guidelines are formulated based on years of experimentations on the bicycle design and their performances. Therefore, these guidelines are considered to be well optimised to ensure the stability and rideability of the bicycle. Nevertheless, these guidelines were mainly proposed for designing big wheel bicycles (wheel size diameter greater than 20-inches). The bicycle frame design is the crucial aspect of their riding performance. Especially, the position of the rider and the geometry of the front steering assemblies determines the performance of a bicycle. According to the current bicycle design practice, most of the design parameters related with the ergonomic are selected using cyclist’s anthropomorphic measurements and steering parameters such as headtube angle, trail and fork offset are selected within a certain range. For example, most of the bicycle is designed with headtube angle ranging from 65 0 to 75 0 and trail ranging from 50-70 mm, and fork offset is generally maintained around 45 mm. Often, the trail values are regarded as a stability indicator. A longer trail is often recommended for better stability. However, there are very limited information in published documents regarding detail guidelines for selecting appropriate head tube angle and trail. As the bicycle manufacturing has become a global industry, the International Organization for Standardization (ISO) also has developed some guidelines for bicycle design for safety and stability. The ISO standard also uses headtube angle, trail or fork offset as the governing parameters for the Milan Paudel, Fook Fah Yap, Anil K. Bastola Dynamic Stability Assessment of Different Wheel Sized Bicycles Based on Current Frame Design Practice with ISO Requirement for Bicycle Safety B World Academy of Science, Engineering and Technology International Journal of Sport and Health Sciences Vol:12, No:9, 2018 366 International Scholarly and Scientific Research & Innovation 12(9) 2018 scholar.waset.org/1307-6892/10009487 International Science Index, Sport and Health Sciences Vol:12, No:9, 2018 waset.org/Publication/10009487