Building a better bike

Racing bicycle design has often taken its lead from the aeronautical industry, but aircraft manufacturers might now have a thing or two to learn from bike builders

THE EQUIVALENT OF six bags of sugar. That is about how much a top-end racing bicycle weighs today thanks to the use of technology originally developed to meet the exacting standards set by the aeronautics industry.

The past decade has seen remarkable changes in the design of high quality bike frames, says Terry Dolan of Dolan Bikes. His company, based outside Liverpool, supplies the bikes used by the An Post Seán Kelly professional racing team. The change is based on a switch from steel and aluminium frame tubes to carbon-fibre technology. “All the professionals could have whatever they want, but they all want carbon fibre,” says Dolan.

Originally metal was the only choice, but things have changed. “We design and build all our frames,” he says. “The last eight years have gone towards carbon fibre. We have a facility in Taiwan to manufacture the frames and forks.” The main reason for using carbon fibre is its incredible strength compared to its weight, but the finished bike still has to perform. “The design of the frame has to be functional as well as light. The weight is important, but [carbon fibre] is just easier to ride. It is not as hard on the body and is very responsive.”

Professional cyclists have the aero-industry to thank for the change. Its motto has always been “light but strong” when trying to develop materials suited to passenger aircraft, says Dr Conor McCarthy of the University of Limerick. McCarthy has spent 15 years researching specialised materials for use in aircraft manufacture, and is now co-ordinating an EU-funded project that has him working with carbon-fibre bike frames.

McCarthy is based in UL’s Department of Mechanical, Aeronautical and Biomedical Engineering and works with its Materials and Surface Science Institute and with the Irish Centre for Composites Research.

Composites are materials that combine often very different ingredients to deliver something new with interesting properties. Carbon-fibre technology is a prime example of a composite, he says.

“You take small fibres of carbon, seven microns in thickness, or sometimes glass fibres, and embed them in an epoxy resin matrix. It bonds the fibres together.” The epoxy gives toughness, while the fibres provide strength, McCarthy says, and the material is extremely light. Extra strength can be added by building up layers, with the fibres laid down in different directions, but the finished material is still thin, strong and lightweight. Carbon-fibre aircraft skin might have 15 or 16 layers, he says, but a finished fuselage panel is still just 1.6mm thick.

Manufacturers such as Airbus and Boeing are increasingly turning to carbon fibre, and new aircraft such as the Airbus A350 and the 787 Dreamliner both use carbon fibre in their fuselages and wings.

“There is a huge amount of research going on,” says McCarthy. “Our speciality in Limerick is looking at joining composite materials.” This is how he became involved in bike research. Bicycles provide a good model for the joining of composites and attachment of metallic components, but also for the use of composites in a complex structure.