“Many higher-end bike frames include carbon, but the key to the R5ca’s design is the use of highly tailored composite fiber architecture,” Guichard says. The fiber architecture is mainly carbon/epoxy prepreg (typically 80 g/m2) made with 6K MR60 intermediate-modulus carbon fiber supplied by Newport Adhesives and Composites Inc. Because pitch-based fibers generally provide better stiffness than PAN-based fibers, the team specified pitch-based YSH60A carbon fiber from Nippon Graphite Fiber Corp. in a few critical areas, such as the sides of the down tube, to increase lateral stiffness.
Next came performance testing. Guichard says most bike lab tests don’t reflect reality and make incorrect assumptions about where each tube on a bike frame carries the most load during certain ride conditions. So, his team conducted more than 15 rigorous strength and stiffness tests, including some that were customdesigned to represent actual cycling conditions. Some of the tests also took into account different riding styles such as vigorous “out of the saddle” pedaling, which puts strain on the bike’s chain stays, down tube and bottom bracket.
The bottom bracket, which puts significant load on the rear of the frame, was redesigned with a wider stance and larger tube diameters to help maximize stiffness. Also, the new bottom bracket design included bulkhead walls in the part’s interior, enabling the outer surfaces to be thinner.
“The result is a frame that is lighter than any other production frame yet is rock solid in pedaling stiffness, cornering and handling,” Guichard says. The R5ca is the stiffest-performing frame Cervélo has ever made, yet the company was able to reduce the weight by 25 percent while still meeting or exceeding all strength requirements, he says.
Using Experience as a Pedal
Guichard says Cervélo’s R5ca bike frame, which won a 2012 Award for Composites Excellence (ACE) Award for Most Creative Application at the ACMA’s COMPOSITES 2012, has significantly advanced cycling technology, thanks to composites and composite design. He also says the project lays the groundwork for future bike frames the company can develop.
“As any composites professional knows, over time the features and technologies of any successful product trickle down to other products,” Guichard says. “Our experience testing and developing the R5ca can help Cervélo improve the overall performance of future frames and bicycles. We continually aim to improve performance, and composite materials are helping us push the limit of what we can accomplish.”