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Aerodynamics and bike fit for speed

Jul 28, 2009
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How fast you finish the cycling portion of a race depends on the power you’re able to produce during the ride. Ultimately, power output depends on just two variables: force and speed. Very simply, it depends on how hard you push and how fast you pedal. The three forces you need to overcome to move forward are air resistance, rolling resistance, and, on climbs, gravity. Because gravity and rolling resistance depend on weight, most cyclists try to minimize weight. This is most easily achieved by using a lighter bike and componentry, but these come at a high cost. Rolling resistance also depends on the road surface, as well as the make, thickness, and pressure of your tires. The biggest resistive force, however, is air resistance, which is dependent on your speed and frontal surface area. At 20 miles per hour on a flat road (gravity is zero), rolling resistance makes up less than 25 percent of the total resistance, while air resistance makes up more than 75 percent. The most effective way to reduce air resistance is to draft behind (or even next to) another rider. For a triathlete without the option to draft (drafting is not permitted in most amateur triathlon racing), reducing frontal area has the greatest effect on performance. Aerodynamic equipment--such as bike frames with tear-shaped tubes, deep-dish wheels and discs, narrow water bottles, tight skin suits, and streamlined helmets--can reduce some of the frontal area. However, a rider’s body is by far the biggest obstacle. Bike fit for a triathlete is therefore optimized with biomechanical fit and aerodynamic positioning; many triathletes even choose to ride a less comfortable....
http://mytriathlontraining.com/content/aerodynamics-and-bike-fit-speed