Racing Bicycle - Racing Wheels and Tires

Racing Wheels and Tires

Most road racing bicycles use 700C bicycle wheels (622 mm bead seat diameter) with matching 20–25 mm wide tires. 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.

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 wattage. 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."

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.