New High Tech Bike Seat Helps Cut Costs
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- Welcome to more rider comfort at 30 percent less weight, thanks to the CFRP-based spring-loaded seat post.
- (© Fraunhofer)
Carbon fiber composite materials (CFRP's) not only help to make cars and airplanes lightweight - they can also enhance valuable lightweight bicycle parts. At the Composites Europe trade show in Stuttgart from October 27 to 29, Fraunhofer researchers will present a spring-loaded seat post made of CFRP's.
Roadside features such as curbstone edges, potholes and streetcar tracks rattle the nerves of any bicyclist, hence professional and recreational cyclists alike have taken to using spring-loaded seat posts. They absorb the worst shocks, and make the ride more comfortable for the back. But for a significantly more comfortable ride, cyclists must delve very deeply into their own pockets.
Made in Pfinztal
Fraunhofer researchers have however just developed a functionally-integrated bicycle seat post from carbon fiber composite materials known as CFRP's, or carbon fiber reinforced plastics, that is ultra light and extraordinarily effective. It recently earned the Eurobike Award at the Eurobike 2009 trade show in Friedrichshafen.
"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, meaning that the CFRP seat post can turn any mountain bike without rear-wheel suspension into a fully spring-loaded luxury vehicle.
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. "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."
Easy to use
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. Up until now, the only seat posts featuring this structure were extremely expensive.
And in this Fraunhofer invention the unique characteristics of carbon fiber composites are combined with an intelligent construction approach that delivers noticeable added cushioning and resilience. 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. This provides, "more ride comfort at 30 percent less weight," says Geiger.
Ready to roll
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," is how Belaew describes the manufacturing process.
Experts are presently working on optimizing the tool engineering and manufacturing process for the production of a larger number of units. Production and distribution will soon take over the "carbobike" spin-off.
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