More About Time Trialling...
Most events are fixed distance, being 10,25,50 or 100 miles. There are also fixed time events -12 and 24 hours -with the objective being to ride the furthest you can. Courses are on public roads and are either 'out and back', using a roundabout to turn halfway, or circuits with consecutive left turns.
The general idea of individual riders riding 'against the clock' and ignoring any other rider who they catch (or particularly who catches them) still holds true for the majority of events today but in addition there are a proportion of events which are for teams of 2, 3 or 4 riders who ride together (but ignoring everybody else as above). These are known as Team Time Trials - shortened to 2up/3up/4up TTTs. The basis for this type of event is to simulate a "break" in a road race where riders working together can "escape" from the bunch. The 4-up variation of this has been an Olympic and World Championship discipline but has been superseded by the (more or less) hilly circuit Time Trial.
There are some rules about bikes and equipment. Brake levers must be positioned so that you can get to them quickly in the event of an emergency. You can use triathlon or 'aero' bars. A solid disc wheel is fine at the rear but not the front. Spoked and composite spoked (tri-spoked) wheels may be used in the front and rear wheel positions. You cannot use streamlining devices in any circumstances.