When selecting a high-performance bicycle, professional cyclists and amateur racing enthusiasts give a lot of weight to grams. Lighter bike frames mean easier hill climbs, which can make a difference in close competition. That’s why many North American competitors will use composite bikes in the 2012 Olympic Cycling events, taking place at five different London venues from July 28 to August 12.
But bike designers face a steep challenge: The lighter they make frames, the more they sacrifice stiffness, which riders need for improved safety, speed and handling. To serious cyclists, too heavy means slow, too light means unsafe and too stiff means uncomfortable.
Don Guichard and his engineering team turned that dilemma into innovation. At Vroomen White Design’s Project California research and development facility, the wholly owned engineering group of Toronto-based bike maker Cervélo, the team relied on composites to create what is now a celebrated product.
The Cervélo R5ca bike frame weighs only 675 grams (1.5 pounds) — less than a quart of water — yet yields higher pedaling efficiencies than nearly all frames weighing twice as much. One product review called the frame “a new pinnacle of performance and efficiency in the application of carbon composites to sports equipment.” Cycling publication Tour Magazine gave the Cervélo R5ca its highest rating ever for road bike frames.
“We couldn’t have done this without composites,” says Guichard, director of technology and manufacturing at Cervélo’s research and development facility. “The frame we built demonstrates the leap in performance available when carbon fibers are used to their best advantage.”
Testing and Optimizing for Performance
Optimizing a racing bicycle for ultimate performance isn’t simple, Guichard says, because the requirements to do so are numerous and often conflicting. For example, a lighter bike frame is generally more desirable, but to meet international racing safety criteria, a frame also must exhibit high strength and the ability to absorb energy from a headon impact.
To reach a new standard in bike frame engineering, the Cervélo team realized it would need to use design and analysis tools, test the structure of a range of carbon fibers and pour its accumulated carbon-manufacturing experience into the project.
“We felt that by choosing the right fiber and direction in different areas, we could uniquely take advantage of carbon material,” Guichard says. “The right fiber orientation and cross-section design was going to be critical. Those factors enable rides to be relatively comfortable compared to other kinds of frames.”
Engineers began with Cervélo’s Squoval (square oval) concept for a road bike, which moves material away from the frame’s center plane, yielding greater stiffness with less material. They input the model of the initial frame into a preprocesser tool, which created a rough finite element (FE) analysis grid that kick-started design ideas. The tool also enabled engineers to analyze tube shapes and material lay-up under various loads.
The team then conducted another FE analysis, inputting preliminary results into the modeling software to create a more detailed shell model of the frame. It also performed a ply-by-ply analysis of more than 300 individual carbon patterns.