A TT bike, or time trial bike, is a type of racing bicycle designed for individual races against the clock. Compared to a road bike, a TT bike is more aerodynamic, has a shorter wheelbase, and puts the rider closer to the front of the bicycle. TT bikes may have either a solid disc or spoked wheels, and they are designed to reduce drag and increase speed, which is critical in time trials where drafting behind other cyclists is not permitted.

The geometry of a TT bike is different from that of a road bike, with specialist handlebars that coerce the rider into a more aerodynamic position. The brake levers on TT bikes are typically located on the end of the bullhorns, so the rider does not have immediate access to them while using the extensions. TT bikes are not suitable for bunch riding, except for the team time trial.

TT bikes have to follow International Cycling Union (UCI) rules, which require that the saddle nose of the TT bike must be 5 cm from the center of the bottom bracket. The UCI also introduced a set of strict regulations around how road, time trial, and track bikes could be designed and what positions riders could adopt on those bikes.

In summary, a TT bike is a specialized racing bicycle designed for individual time trials. It is more aerodynamic than a road bike, has a shorter wheelbase, and puts the rider closer to the front of the bicycle. The geometry of a TT bike is different from that of a road bike, with specialist handlebars that coerce the rider into a more aerodynamic position. TT bikes have to follow International Cycling Union (UCI) rules.