The carbon composite seat post results in a more comfortable ride.
The carbon composite seat post results in a more comfortable ride.

Fraunhofer will exhibit in Hall 4 on booth D04 at the COMPOSITES EUROPE trade show in Stuttgart, Germany, on 27-29 October.

For many years, professional and recreational bikers have been using spring-loaded bicycle seat posts to absorb shocks for potholes etc, and make the ride more comfortable. Fraunhofer researchers claim to have developed a bicycle seat post made for carbon fibre reinforced plastic (CFRP) that is extremely lightweight but very effective.

“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.

The CFRP component earned the Eurobike Award at the Eurobike 2009 trade show in Friedrichshafen, Germany, in September. It has also been nominated for the 2009 AVK Award for Innovation, which will be announced during COMPOSITES EUROPE.

The carbon composite seat post was designed at the Fraunhofer-Institute for Chemical Technology ICT in Pfinztal, Germany, 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. “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 mm range. That tangibly augments rider comfort.”

The outer radii of the profiles were chosen so that riders could easily mount the component onto existing bike frames. 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. Until now, the only seat posts to feature this structure were extremely expensive.

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.

“More ride comfort at 30% less weight,” says Geiger.

The prototype of the CFRP seat post was manufactured through a resin transfer moulding (RTM) process.

“First, you fit the braided cable sleeves like a sock onto the mould core – a butyl sleeve – and stretch them until you get to the desired fibre angle," explains Belaew. "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."

The researchers are now working on optimising the tool engineering and manufacturing process for the production of a larger number of units.