With this year's Tuesday Night Time Trials (TNTT) starting May 1st its appropriate to ask:
WHAT IS A TIME TRIAL?
A time trial is a road bicycle race in which cyclists race alone against the clock. Time trials are also referred to as "the race of truth", as winning depends only on each rider's strength and endurance, and not on help provided by team-mates and others riding ahead and creating a slipstream. Starting times are at equal intervals, usually one or two minutes apart. The starting sequence is usually based on the finishing times in preceding races with the highest ranked cyclist starting last. Starting later gives the racer the advantage of knowing what time they need to beat (and also makes the event more interesting to spectators). Competitors are not permitted to draft (ride in the slipstream) behind each other. Any help between riders is forbidden. The rider with the fastest time is declared the winner.
Specialized aerodynamic time trial bicycles, clothing, helmets, aerobars and other equipment are often used in ITT events. Generally, components are designed to be as aerodynamic as possible, as most of the rider's effort goes into overcoming aerodynamic drag. The rider's position makes the greatest difference, and most use the now-standard tuck position, using tribars to allow the rider to position their arms inline with the wind and allow their back to sit as low and flat as possible, reducing frontal area and improving air flow around the body. TT bikes often have lower handlebars than normal road racing bikes to facilitate this. Also, the saddle is sometimes moved forwards relative to the handlebars and bottom bracket to allow the hips a more natural angle of motion, improving performance (for UCI-sanctioned events, the saddle must be a certain distance behind a vertical line drawn through the centre of the bottom bracket).
Equipment used is very specialized, and component manufacturers can spend vast sums of time and money on wind tunnel testing to ensure their product is faster than the competition's. Deep section or solid disc wheels are often used to reduce turbulence around the spokes, but these can affect handling in windy conditions. In the UK the front wheel must have a minimum of 45% open area when viewed from the side, for safety reasons. UCI events still permit the use of disc wheels for the front, but it is very unusual. Many components are modified for aerodynamic efficiency, and manufacturers are now developing more integrated systems, such as brakes built into the fork or frame so as not to disturb the airflow.
Clothing is also different for time trialling. One-piece skinsuits that do not flap in the wind are common; tight lycra shoe covers help improve airflow over buckles and straps; long pointed helmets channel air down the riders back (the position of the helmet above the rider's back is crucial, it must be as close to the body as possible; too high and the air will just flow underneath the helmet. This is often hard to achieve as the rider moves his head due to the suffering endured during a hard race).