International Journal of Human Movement and Sports Sciences 5(4): 77-84, 2017 http://www.hrpub.org DOI: 10.13189/saj.2017.050403 Impact of Wheel Size on Energy Expenditure during Mountain Bike Trail Riding Julie E. Taylor, Camille Thomas * , Jacob W. Manning College of Education and Human Development, Southern Utah University, United States Copyright©2017 by authors, all rights reserved. Authors agree that this article remains permanently open access under the terms of the Creative Commons Attribution License 4.0 International License Abstract This study examined the energy expenditure during mountain bike trail rides on a 26-inch wheel (26er) compared to a 29-inch wheel (29er). Thirteen experienced bikers (four women, nine men, age=33.0±10.1 yrs), completed similar 6.7km trail rides on a 26er and 29er. GPS was used to measure distance and speed during each ride. Energy expenditure was determined by measuring oxygen consumption. Compared to the 26er, the 29er rides took less total time (24.2±3.2 vs. 25.5±3.5 minutes, p=0.015), hence faster speeds (4.7±0.6 vs. 4.4±0.6 m·s -1 , p=0.022), lower average heart rates (155.0±19.2 vs. 162.2±16.8 bpm, p=0.047), and lower total calories (263.3±34.3 vs. 290.7± 36.9 kcals, p=0.001). Work rates represented by the rate of oxygen consumption (ml O 2 ·min -1 , p=0.65) were not different. At similar work rates, riders apparently gained a mechanical advantage on the 29ers allowing for 5% lower riding times and heart-rates, 6.8% faster speeds, and a 9.4% reduction in the total caloric expenditure for a standardized trail ride. Keywords Caloric Cost, Cycling, Wheel Diameter, Cross-country Biking, Performance 1. Introduction Mountain bikes with 26-inch diameter wheels (26er or 559mm ISO) were the industry standard for decades. More recently, mountain bikes with larger circumference and fatter wheels have gained popularity. One of the most common modifications is alterations in wheel diameter or size. Bikes with 29-inch diameter wheels (29er or 622mm ISO) are now very common. In countries where the metric system is the standard for weights and measures, the terms for mountain biking wheel diameter is still often reported in inches and is well understood. Therefore, the terms 26er and 29er to describe wheel diameter will be used throughout this report. Anecdotally, experienced mountain bikers have claimed that the 29er “rolls over” obstacles more easily requiring less energy to ride. In other words, the 29er may have a lower rolling resistance and, therefore, less energy is needed to maintain speed. Previous research, when examining road bikes, found that a larger wheel diameter had a lower rolling resistance than smaller wheel diameters [1, 2, 3]. Moreover, Steyn and Warnich [4] reported that the 29er had less rolling resistance compared to the 26er on soft surfaces such as sand, with little difference on hard surfaces such as rock or asphalt. Given that most mountain biking trails include a combination of terrain surfaces, the difference in rolling resistance may translate into a difference in total energy expenditure and speed of riding. Another possible advantage to the 29er might be the conservation of angular momentum because of rotating mass. When wheels hold their momentum over a combination of terrain as opposed to changing momentum, mountain bikers will use less energy and obtain faster times. According to Newton’s laws of motion, a heavier rim would maintain a more constant speed, such as the 29-inch wheel. In other words, the 29er requires less energy to maintain momentum. Macdermid, Fink, and Stannard [5] found that 29-inch wheels showed a clear performance advantage during hill climbs, agreeing with the theory of angular momentum. In summary, the 29er may maintain angular momentum because the rotating mass reduces deceleration over the rough and rocky terrain. On the other hand, 26ers may decelerate to a greater extent over rough and rocky terrain causing the rider to expend energy to re-accelerate. Reduced rolling resistance on some trail surfaces and the maintained angular momentum of the 29er could offer an advantage in energy expenditure. Currently, only one study has directly examined energy expenditure when riding a 29er versus a 26er. From unpublished results, Hurst [6] found no significant difference between elite riders’ energy expenditure for the 29-inch, 27.5-inch, and 26-inch wheels during a 3.48km (2.16 miles) mountain bike course. Hurst measured elite competitive cyclists at race pace and, therefore, the results may not be generalizable to recreational cyclists that are not highly trained. Hurst also reported that the 29er was