A racing bicycle, also known as a road bike is a bicycle designed for competitive road cycling, a sport governed by and according to the rules of the Union Cycliste Internationale (UCI). Racing bicycles are designed for maximum performance while remaining legal under the UCI rules. They are designed to minimise aerodynamic drag, rolling resistance, and weight, and balance the desire for stiffness for pedaling effiency with the need for some flexibility for comfort. Racing bicycles sacrifice comfort for speed compared to non-racing bicycles. The drop handlebars are positioned lower than the saddle in order to put the rider in a more aerodynamic posture. The front and back wheels are close together so the bicycle has quick handling, which is preferred by experienced racing cyclists. The derailleur gear ratios are closely spaced so that the rider can pedal at their optimum cadence. However, racing bicycles must retain the ability to maneuver safely within a tightly-packed peloton, and be sufficiently comfortable to ride for races of six hours or more. Bicycles and most wheels ridden in professional competition must be type-approved by the UCI, and made available for commercial sale. It is common for professional road cycling teams to use prototype bicycles and equipment before they become commercially available. Racing bicycles are generally legal for use on public roads and are widely used for non-racing fitness and utility riding. Distinction between road bicycles and others Bicycles for racing on velodromes are track bicycles; bicycles for racing off-road are mountain bicycles, cyclo-cross bicycles, gravel bicycles or cycle speedway bicycles; bicycles that race according to the rules of the International Human Powered Vehicle Association include faired recumbent bicycles which, on flat ground, are the fastest bicycles in the world. Recumbents were excluded from the UCI definition of a bicycle on 1 April 1934. Time trial bicycles are a subset of road bicycles that are designed for time trial events. The UCI rules for these bikes are slightly less prescriptive than those for "massed start road races" (see rules 1.3.020 to 1.3.023). Triathlon bicycles are governed by International Triathlon Union (ITU) rules, which allow more recent technological developments than do the UCI rules. Owing to the lower air resistance and better body stance for pushing, road bicycles tend to be more efficient for use on smooth roads. Cyclo-cross bicycles, which are used for racing on off-road circuits, are closer to racing bikes than to