Today’s bikes are far more sophisticated. As its name suggests, carbon fiber is usually formed as thread and then woven into a fabric. Frames are now built in molds, enabling exotic and aerodynamic shapes within the limits set down by the International Cycling Union. By manipulating the carbon-fiber fabric used in different parts of the frames, manufacturers can stiffen it in some areas, such as around the cranks, while building in flexibility for rider comfort in areas where it will not affect performance.

Once the fabric is in place, it is coated with epoxy, effectively creating a carbon-reinforced plastic bicycle.

Bicycle manufacturing has largely moved to Taiwan and China, regardless of the country of origin of a brand name. While the American bike company Trek and Toronto-based Cervélo produce a comparatively small number of their highest-end frames in the United States, most of the bikes at the Tour were made in Asia and are identical to those available to any cyclist with enough money.

Michael Kaiser, the head of product development at Canyon, a German company that offers both carbon and aluminum bikes, and provides bikes to two teams at the Tour, said that with carbon, careful manufacturing was as important as design.

“To get exactly the right result is more demanding than with metals, as it requires a comparatively large degree of work by hand,” he wrote in an email. “Therefore the entire manufacturing process has to be incredibly precise with extensive quality controls in place to ensure there are no defects in the parts.”

To that end, Canyon has been using CT scanners to discover hidden defects in its forks, a potentially lethal point of failure, and will soon do so on frames.

Chris Riekert, a spokesman for Specialized, an American company that supplies bikes to three Tour teams, said in a statement, “Carbon gives our engineers the ability to produce much stronger and lighter products than traditional steel or alloy by letting us put more material in high stress areas to ensure performance and safety in real world riding conditions.”