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The Rise of Carbon Fiber

By Patrick Brady

Carbon fiber is the dominant material for constructing high-performance racing bikes today. It has supplanted aluminum, steel and even titanium as the material of choice for the world's top professionals. No other material can match carbon fiber for its extraordinary combination of light weight and stiffness while preserving a rider's comfort for long races. But carbon fiber wasn't always top dog; its success is due to a number of relatively recent advances.

Felt Bikes For nearly 100 years bicycle frames were made from steel. From kids' bikes to 3-speeds to the bikes winning the Tour de France, steel was very nearly the only material used. The reasons for steel's popularity were simple enough: the strongest alloys were relatively light, reasonably inexpensive, plentiful and easy to work with.

Beginning in the 1980s manufacturers began offering bicycle frames made from materials other than steel. Aluminum came first, followed by titanium. Tubes made from carbon fiber were occasionally glued to aluminum lugs, but the material's promise was first hinted at when a group of engineers introduced the first molded carbon fiber frame in 1987.

Carbon fiber is different from other materials used to make bicycle frames because it can be molded into any shape that can be imagined. This allows an engineer working with the material to design for stiffness where it is most necessary and compliance, or flex, where it most helpful. Fortunately, bicycle designers had a wealth of experience.

Working with steel demands creativity. Over the years, metallurgists created new alloys with greater strength. Engineers learned to thin the midsection of tubes, called butting. They learned to swage (say swej) tubes in order to taper the tubes to give different levels of compliance over the length of the tubes and to dissipate vibration before it reaches the rider. Ovalizing allowed engineers to make tubes stiffer laterally or vertically. Each of those lessons has contributed to the improvement of the carbon fiber bicycle.

Slipstream-Chipotle presented by H3O is the largest and most powerful of the American teams at the Amgen Tour of California. The team's bicycles are produced by California-based Felt Bicycles. Here's how the engineers at Felt have applied those lessons:

As superior carbon fiber material has become available to the sporting goods industry (thanks in part to the golf and tennis industries' demand for the same materials), cutting edge cycling companies have incorporated those materials into their frames. These materials can be very expensive and aren't appropriate for use in every area of a bicycle frame or fork, but as our understanding of the stresses placed on a frame has increased, so has our ability to judge what materials should be used and where. In Felt's Ultra Hybrid Carbon, its engineers blend different materials based on the frame's needs in each location, something that cannot be done with steel-there is no way to blend multiple types of steel in a single tube.

The lessons learned in butting steel tubes still apply: the best frames will feature more material at tube junctions, but carbon fiber allows butting to be performed at a much more sophisticated level. A steel tube's thinnest section is governed by how thick the butt is; the thin section must be more than 60 percent of the thickness of the butt. Carbon fiber has no such restriction; in Felt's top racing frame, the F1, the thickest sections are more than three times as thick as the thinnest section.

And because the loads placed on a tube vary according to the tube's placement and even vary along its length, tubes are now shaped to withstand the loads placed on a bicycle, whether the rider is pedaling in the saddle, cornering, sprinting in the drops or braking for a stop. On the Felt F1, the downtube is as wide as possible at the bottom bracket in order to offer stiffness when sprinting.

Between the new materials offered, the advanced in material placement and the shapes into which the materials are formed, today's carbon fiber road bike is stiffer, lighter and more comfortable than its predecessors.