Time trial frames are made for speed. In time trial races the rider is not allowed to draft (ride in another riders slipstream) which therefore means the emphasis needs to go to aerodynamics and materials used. To aid the aerodynamics the front forks are very flat, helping to cut through the air, and the vertical down tube is often shaped to the rear wheel and within millimetres of the tyre.
Time trial or TT bike frames are normally made from one of three different materials. They are:
The pros are that steel frames are relatively inexpensive, strong and easy to work with. The con is that it is quite heavy, making it less competitive for those seriously into their triathlons or time trial riding.