You’ve probably seen it: a cyclist racing against the clock on what looks like a futuristic rocket bike. But the faster they go, the more air resistance they encounter. When racing against the clock, the emphasis is on cheating air resistance as much as possible through aerodynamics.
Aerodynamics is a very complex subject, but one important aspect is frontal area. Frontal area is the surface area of the rider and bike, looking from the front. It’s easy to see how this can be reduced to improve aerodynamics: simply rotate the rider’s torso out of the air stream. This is where many people get themselves into trouble. The rider is still the motor, and aerodynamics don’t count for much if this motor doesn't efficiently deliver power to the back wheel. If you rotate the rider's torso too far, the hips start rocking on the saddle, wasting lots of energy in the process. The solution is to take some angle out of the hips by moving both the saddle and the handlebars forward. This is the basis for the triathlon and time trial positions.
Proper fit on a triathlon or time trial bike is even more important than on a standard road bike. How you set up the bike depends on how long the event is and how hilly the event is. Longer events put the emphasis on comfort while short events are about pure speed. Hills require torque which means the body needs to be leveraged over the pedals, so the rider needs to be more upright. Flat courses put the emphasis on aerodynamics and getting the rider’s frontal area as low as possible. In a triathlon, no amount of speed will matter if you get off the bike and can’t run.
Bike designers put a lot of research into improving the aerodynamics of their bicycles. As with standard road bikes, there are also many options for materials, frame geometry, and components. Choosing a triathlon or time trial bike is a process of deciding which of these designs best helps you achieve your goals, while accomodating your specific position.
Ed Sassler of Belmont Wheelworks says: