The cycling section of a triathlon is a completely different animal than a traditional road race. This style of race moves at a faster pace over a much shorter distance. Cyclists in triathlons use a specialized bicycle called a tri bike designed for sprints for these quick sections. A tri bike is heavier than a road bike but is much more aerodynamic and utilizes a different riding position to maximize performance at high speeds. This makes it the best choice for a cycling sprint during a triathlon, because it will be faster and more efficient than a traditional racing bike.
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Ride Like the Wind
The sprint of a triathlon is a battle against air resistance. Next to the force of gravity on an incline, air resistance is the greatest force a cyclist needs to overcome, accounting for up to 90 percent of the resistance felt during a sprint. This makes the aerodynamics of a tri bike much more important than the aerodynamics of a road bike, which is designed for endurance races over a wide variety of inclines. To further improve aerodynamics, tri bikes also place the rider in a different position that maximizes pedaling power and minimizes the profile of the rider.
A tri bike uses aerobars to allow a much more aggressive riding position. Aerobars are either integrated into the handlebars on a tri bike, or come as an attachment to bullhorn bars using clamps. These bars have elbow pads so that the rider can place his arms in a bent position, tightening up their profile for the best aerodynamics. In this position, your pedaling efficiency is still excellent, making it ideally suited to sprints that require a lot of power.
Life in the Slipstream
A tri bike is usually built from carbon fiber, which consists of individual fibers sealed into plies using a laminate. Carbon fiber is extremely stiff and lightweight, and can be shaped much easier than an alloy. This allows a tri bike to have a unique shape that minimizes air resistance using wing-like tapering in each section of the frame. The seat tube of the frame will usually curve around the rear wheel, giving the bike a smooth, continuous shape. The frame of a tri bike is usually heavier than a traditional road bike frame because of the extra material used in making the aerodynamically shaped tubing, but weight has a much smaller effect on speed than aerodynamics at the high speeds of a triathlon sprint.
Reinventing the Wheel
Tri bikes use carbon fiber wheels with deep rim widths to further improve aerodynamics. Some riders take this to the extreme by using a fully enclosed rear wheel, which covers the spokes in a carbon fiber dish. These wheels cut through the wind in the same way the frame's shaping does, reducing the turbulence caused by rotating spokes.