Triathon bikes come in all shapes and sizes and are designed to suit the various distances and courses that are the very essence of tri. What is certainly true for all tri bikes is that they are not subject to the same stringent UCI design regulations that limit how aerodynamically efficient a bike can be.
The first and most popular option for triathlon racing is the TT bike. This type of bike allows the rider to assume an aero tuck position that helps to reduce the frontal area that is subjected to the airstream. After all, the rider is responsible for creating approximately 75% of all the drag. In terms of appearance, they look very similar to a normal time-trial bike. What separates a tri bike from a TT bike, however, is certain aero-enhancing modifications that improve how air flows around the bike and rider.
The most obvious difference to a road bike, even to the casual observer, is the tube profiles. Each tube is shaped in such a way that it alters how the air reacts when it flows over the tube with the goal of keeping drag to a minimum. Other notable differences include the addition of fuel and storage boxes which serve a dual purpose. Not only can energy food and tools be stored but the shape of the boxes themselves act as aerodynamic fairings.