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CFRP Seat Gives Full-Suspension Feel

30 October 2009

At this year’s Composites Europe, Stuttgart, researchers from Fraunhofer presented its latest development in carbon fibre bicycles - a spring-loaded seat post made of CFRP’s.

The prototype of the CFRP seat post was manufactured through a Resin Transfer Molding (RTM) process. “First, you fit the braided cable sleeves like a sock onto the mold core – a butyl sleeve – and stretch them until you get to the desired fiber angle. After pumping up the tubes as defined, a resin-hardening mixture infiltrates the component. As the hardening begins, the pressure on the butyl tubes is increased again, in order to achieve maximum impregnation,"" says Sergei Belaew who worked on the project.

Spring-loaded seat posts are not a new idea; they have been used for years in professional and recreational bikes as a method to cushion the rider from potholes and curbs. However, a post made from CFRP will add several benefits to the ride, most notably reducing its overall weight. However, it is said that the effect of this particular design can make the bike feel like it has additional suspension.

“A hardtail mountain bike with this new kind of CFRP seat post rides as if it were a full suspension bike,” says triathlon world champion Daniel Unger after a test drive. It is this kind of testimony that helped the component to earn the Eurobike Award at the Eurobike 2009 trade show in Friedrichshafen and in Stuttgart, the high-tech post has been nominated for the 2009 AVK Award for Innovation.

It is believed that the unique characteristics of carbon fiber composites, combined with a keenly intelligent construction approach, delivers noticeable added cushioning and resilience. Researchers claim that the deflection of the CFRP profiles influences the motion of the seat tip, and under ideal conditions actively supports pedaling. In addition, the post alleviates peak loads, even around minor superficial bumps – tar spots, damaged street surfaces and manhole covers are barely noticeable.

The seat post was designed at the Fraunhofer-Institute for Chemical Technology ICT in Pfinztal as part of Fraunhofer's innovation cluster known as “KITe hyLITE – Technologies for Hybrid Lightweight Construction”. “The impetus for this came from our colleague and bicycle enthusiast, Sergei Belaew,” recalls group manager Oliver Geiger, who handles the implementation of the flexible seat post in Professor Frank Henning's department. “The component is based on two CFRP profiles that work like laminated springs. In this respect, the spring rigidity was calibrated to keep the deflection within the 10 to 15 millimeter range. That tangibly augments rider comfort.”

According to designers, the outer radii of the profiles were chosen so that riders could easily mount the component onto existing bike frames without a hitch. The saddle rail is articulated at the upper end of the profile; together with the clamps and the seat, the configuration results in a parallelogram.






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