# Aerodynamic Benefits by Optimizing Cycling Posture
## 1 Introduction  
Aerodynamic drag is crucial in cycling. It is one of the most limiting factors and therefore, bears the greatest potential for improvement [1; 2]. For many professional cyclists and triatheltes, it is about saving energy as much as possible. Those savings can be achieved by riding in a group or optimizing the cycling posture. In a team time trial event or in a small group of up to nine cyclists riding at the same speed, savings of up to 50-60% can be observed, depending on the cyclist's position and distance from the teammate in front [3]. In large pelotons, groups of 100 plus riders, the effect multiplies and becomes even more significant. Savings and drag reductions of 5% for an isolated cyclist at the back of the peloton can be found. These cyclists hardly have to pedal at common racing speeds of 15 m/s (54 km/h). Not only does the cyclist at the back of the peloton experience a drag reduction, but the leading cyclist does, due to the upstream flow disturbance caused by the riders behind him/her [4].  
Knowledge about aerodynamic drag is not only used in professional road cycling, it also in related sports such as the triathlon, especially in long distance/Ironman (IM) events. An IM consists of a 3.8 km swim, followed by a 180 km bike ride and a closing 42.2 km marathon run. In this case, saving energy for the upcoming run is decisive. Despite the fact that drafting, i.e., direct riding behind one and another, is strictly forbidden in these events, refs. [3; 5] indicated the benefits of riding 10 m behind a competitor, within the permitted range.  
At racing speeds of 15 m/s, the aerodynamic drag makes for up about 90% of the total resistance [6; 7; 8]. This major part is split into two components: 70% is due to the cyclist and 30% is due to the bike [9]. Since the majority of the aerodynamic drag of the athlete iscaused by the athlete's body itself, different cycling postures will have significant effects on the speed he/she is traveling at [8,10,11]. Thus, even relatively small changes in posture, such as changing arm position, can result in noteworthy savings [12].  
Our main purpose was to quantify the impacts of four positions and present them by showing the resulting time savings on the 180 km IM World Championship course in Hawaii, considering realistic yaw angles of 0-20\({}^{\circ}\). The elevation profile and weather data of the IM Hawaii bike course are well known, so the course is highly suitable for this work. For this purpose, a 3D scan of a professional male athlete was performed, and different cycling postures were observed. As a low cost approach and novelty presented in this work, the scan was performed by using a commercially available iPhone 12 Pro with a LIDAR Scanner. The scan was then post-processed using the open-source Software Blender. Flow simulations were run in Nabla Flow's in-house simulation software AeroCloud, an OpenFoam-based CFD tool.  
Comparable investigations have been conducted by [13, 14, 15] to name a few. [PERSON] et al. [15] have the most recent excellent review on the importance of bluff-body aerodynamics for _elite level cycling_, as they called it.