A racing bicycle, also known as a road bike, and once popularly known as a ten speed, is a bicycle designed for competitive road cycling, a sport governed by and according to the rules of the Union Cycliste Internationale (UCI). The UCI rules were altered in 1934 to exclude recumbent bicycles.
The most important characteristics about a racing bicycle are its weight and stiffness which determine the efficiency at which the power from a rider's pedal strokes can be transferred to the drive-train and subsequently to its wheels. To this effect racing bicycles may sacrifice comfort for speed. 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. The derailleur gear ratios are closely spaced so that the rider can pedal at their optimum cadence. Other racing bicycles, especially those used in time trialling, prioritize aerodynamics over comfort.
Bicycles for racing on velodromes are track bicycles; bicycles for racing offroad are mountain bicycles, cyclo-cross 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).
The frame of a road bicycle must, according to the UCI regulations, be constructed using a "main triangle" with three straight tubular shapes--the top tube, down tube, and seat tube. These three tubes, and other parts of the frame, need not be cylindrical, however, and many racing bicycles feature frames that use alternative shapes. Traditionally, the top tube of a racing bicycle is close to parallel with the ground when the bicycle is in its normal upright position. Some racing bicycles, however, have a top tube that slopes down towards the rear of the bicycle; the "compact" frame geometry was popularized by Giant.
Frame manufacturers are free to use any material they choose in the frame. For most of the history of road racing, bicycle frames were constructed from steel tubing, and aluminium and titanium alloys were also used successfully in racing bicycles. Racing bicycles in these three materials are still commercially available and are still used by some amateur racing cyclists or in vintage racing classes. However, virtually all professional road racing cyclists now use frames constructed from various carbon fiber composite materials, and a typical modern carbon fiber frame weighs less than 1 kg (2.2 lbs).
Particularly since the introduction of carbon fiber frames, the shape of the tubes that make up the frame has increasingly diverged from the traditional cylinder, either to modify the ride characteristics of the bicycle, reduce weight, or simply achieve styling differentiation. However, a recent trend in road bicycle frame design is tubing claimed to reduce aerodynamic drag, adopting many design features from time trial bicycles. While many professional riders, particularly sprinters, use "aero road bikes", as of 2018 a substantial fraction of professional racers use bikes with limited or no aerodynamic tube shaping.
Most road bicycles use 700C bicycle wheels (622 mm bead seat diameter) with matching 20-25 mm wide tires. As of 2018, there has been a trend towards wider wheels and tires (up to 28 mm nominal width in some cases), which have been found to increase rider comfort and decrease rolling resistance without unduly affecting aerodynamics.
The wheels greatly affect the performance of a racing bike. The rim of the wheel can be shaped for greater aerodynamic efficiency making a triangular cross-section to form a teardrop with the tire. For hill climbs, however, energy losses due to the higher weight of most aerodynamic rims are greater than the aerodynamic drag reduction that they offer, so a traditional lighter box-sectioned rim is often used to make it go faster.
For aerodynamics and rotating weight, it is generally better to reduce the number of spokes in the wheel. For high-end wheelsets, the spokes can be shaped to have a bladed cross-section, further reducing wind resistance.
The most common material for a wheel rim is aluminum alloy, with molded carbon fiber rims being a popular choice for pro-level racers and enthusiasts. Carbon fiber rims are lighter than the same shape in aluminium, allowing riders to choose "deeper", more aerodynamic rims without an unacceptable weight penalty. Race-grade wheelsets are very expensive and often fragile. Riders who race often choose to own at least two pairs of wheels: a heavier, more durable, and cheaper wheelset for training, and a lighter, more aerodynamic wheelset for racing. Racers with sufficient resources may have multiple racing wheelsets to choose from depending on the course and weather conditions; deeper rims lose their aerodynamic advantage, and are hard to control, in high crosswinds, and on mountainous courses the lightest possible wheelset may be preferred by some riders.
To reduce both air resistance and rolling resistance on the road, tires are lightweight, narrow, and have a thin, smooth tread. They are inflated to a high pressure, typically around 8 bar (820kPa/120psi); track racing tires can be inflated up to circa 14 bar. Until recently, most racing bikes used tubular tires which have no beads: they are sewn around the tube and glued to the rim. These tires provide an advantage in weight (lacking the relatively heavy wire bead), rolling resistance, grip and pinch flat protection, but their greatest advantage lies in the ability to use a very lightweight simple box-section rim, rather than the U-shaped clincher rim. A U-shaped clincher rim must be made of relatively heavier gauge material to prevent the tire pressure from spreading the inherently weak U shape and allowing the tire to come off the rim. Advances in tire technology, however, have seen the far more practical (due to greater ease of changeability) clincher (beaded) tire close the gap. Some manufacturers create tubular-clincher tires, where the tires are sewn around the tubes and have a bead, but there is some debate as to the effectiveness of a tubular-clincher tire. Proponents believe that it has all the advantages of a tubular tire made to fit a clincher rim, but critics argue that the design includes disadvantages inherent to both systems--the rim weight is still high, the tire is more expensive than a standard clincher tire, and repairing a puncture on a tubular clincher is as inconvenient as it is with a standard tubular tire. However, a particular benefit of the tubular-clincher design is that the risk of pinch flats is very low (like the tubular tire), yet it allows the use of the more popular clincher wheel.
Wheel moment of inertia is a controversial subject. In this article: wheel theory, the author does some calculations on wheel effects. Moment of inertia changes result in a decrease in watts of between .004 and .022%, while lower mass provided between .2 and .46%, and better aerodynamics provided between .6 and 1.8% decrease in power. Therefore, wheel moment of inertia effects are neither noticeable nor important. At the same time, a product launched in 2008 to dynamically alter the rotating inertia of bicycle wheels claims to have "outperformed the standard, equivalent wheel by 5.6sec/mile."
Road bike components are collectively referred to as the groupset. The quality of the groupset determines how refined the bike feels, how much maintenance it requires, and contributes to the performance of the bike. The three major groupset manufacturers of complete groupsets for racing bicycles are Shimano, SRAM, and Campagnolo. Some companies only produce specific components of the groupset, such as Full Speed Ahead (often abbreviated to FSA). The companies have different design strategies, and some cyclists have great brand loyalty for one or the other.
In the early 1990s, Shimano introduced dual-control with a system called Shimano Total Integration (STI). STI is characterized by its combined brake and shift levers, or "brifters". Previously, the shifters were mounted on the stem, handlebar ends or the down tube of the frame. Dual control addressed the problem of having to reposition a hand to change gears. STI was followed by the competing Campagnolo/Sachs Ergolever. SRAM uses a technology known as Double Tap for their integrated shifter/brake lever.
In the mid 1990s Mavic, known for their wheelsets, introduced an electronic shifting system which was pioneered in the Tour de France by American Greg LeMond and later on by Briton Chris Boardman, who liked the fact that the system allowed him to shift from his aerobars and his brake levers. The system did not catch on due to technological hurdles. In 2009, Shimano commercially released the Dura-Ace Di2 electronic shifter, and Campagnolo and SRAM followed suit in the early 2010s. As of 2018, the vast majority of top-level professional teams use electronic shifting, as do many amateur riders. Mechanical derailleurs remain popular with amateur racers and recreational riders for cost reasons.
Groupset manufacturers have gradually increased the number of gears on racing bicycles, allowing a greater range between the highest and lowest gears while maintaining relatively small gaps between each successive gear. As of 2018, most racing bicycles used in professional racing have 2 front chainrings and 11 gears on the rear cassette.
Carbon fiber has also become more popular for components. Shimano, Campagnolo and SRAM have introduced carbon fiber for their high-end shifters and brake levers, cranks, and parts of their derailleurs. Carbon fiber stems, handlebars, shoe soles, forks and seatposts are also more commonplace, including integrated stem/handlebar combinations. The advantages of carbon fiber are low weight as well as increased vibration damping leading to a more comfortable ride.
Racing bicycles were required to use caliper brakes by UCI regulation, but manufacturers began producing road bikes with disc brakes for recreational use in the mid-2010s, and their use was trialled in professional racing in 2016 and 2017. Disc brakes offer better stopping performance, particularly in wet conditions. Rider disquiet over the crash safety of disc brakes led to the introduction of versions with chamfered edges to reduce the risk of the rotating disc acting as a cutting blade. In 2018, the UCI concluded the trial and legalised the use of disc brakes in all road racing events. While some professional teams still use caliper brakes, which are lighter and may be marginally more aerodynamic, an increasing proportion of teams have switched to discs as of 2018.
For recreational road cycling, the road-style bicycles with drop handlebars used to be the norm in the 1980s, along with the touring bicycle, (a drop-handlebar bike with a slightly longer wheelbase to provide a smoother ride and less sensitivity to steer and balance disturbances). These designs, called "road bikes" or colloquially, "roadies" or "racing bikes", have become less popular in recent years[when?]. The Mountain bike geometry, with its straight handlebars and upright sitting position (resembling the city bike), have moved into the high-performance spaces, and high production volumes have brought down costs significantly.
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 mountain bikes. They have wider, treaded tires and cantilever brakes instead of caliper brakes but are still less efficient than racing bikes at higher speeds.
The UCI rules currently specify that a road bicycle have the following characteristics:
Note that the regulations regarding the dimensions of the bike are allowed exception, given that the rider can demonstrate a morphological need for the exception based on limb size or other factors.
These rules effectively and purposely rule out recumbent bicycles, and have done so since 1934.
Road bicycles are built for casual recreational use, often labeled as "sportif" bicycles or "dropped-bar fitness bikes". These have much in common with a competitive racing bicycle, but the frame geometry is relaxed to make the bicycle more comfortable over long distances, though less effective for short bursts of speed. They usually have a wider range of gear ratios (with greater gaps between each ratio) and fewer high-tech racing features.
each spoke of a rotating wheel is subjected to a drag force that opposes its motion.