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.

Bike frames undergo different stresses at different locations. When being formed, extra fibres are laid down along areas of high stress, but this is not done on a hit and miss basis. Stress patterns are complex, so mathematical models are used to find areas of stress and a “fibre architecture” is then built to overcome this.

Airlines prefer carbon-fibre composites because, unlike metals, they do not suffer from “fatigue”, a gradual decline in strength that ultimately leads to failure.

Composites, however, do not do so well with sharp impacts such as a bike crash, McCarthy says. Bolted-on metal components, such as the derailleur mechanism that changes a bike’s gears, strike the ground first and do not flex. “It can cause cracks in the joints. That is how I got into bikes because we are looking at [component] joints on a bicycle,” he says. “We are trying to design a joint that, if you crash, the derailleur will break off, without cracking the frame. The derailleur will just decouple.”

A great deal of research also goes into brake, gear and derailleur technology, but this work is dominated by the three main manufacturers, Shimano, Campagnolo and Sram, says Terry Dolan. Carbon fibre cannot help much in this regard because the durability of metal is more important than weight for these components.

* The cyclist’s greatest enemy is drag, having to force a path through the surrounding air. Even with no wind, aerodynamic drag causes 70 to 90 per cent of the resistance when cycling. Tight-fitting synthetic fibres make cyclists more slippy and a shaped helmet can reduce drag.

* Cycling is five times more efficient than walking in terms of energy expenditure. About 2,000 kilocalories will keep most of us going for a day; Tour de France athletes can burn through 10,000 kilocalories when covering up to 240km a day.

* Road friction produces rolling resistance, and this has to be kept to a minimum. Thin tyres at high inflation pressures help to keep a tyre’s road footprint to a minimum. Mountain bikes require a bigger footprint and lower pressure to help them pass over rough terrain.

* All cyclists are familiar with cable-controlled calliper brakes. Mountain bikes often have disc brakes similar to those found in cars for greater braking power. Some set-ups include ceramics, which cope better with the heat caused by high-speed braking.

* A steel frame suits a mountain bike, while lighter aluminium is better for road use. The most expensive frames are now made from carbon fibre composite materials. They are tough but very lightweight.

* Muscles are the engines that drive the bicycle down the road, with those of the calf and the back of the thigh doing most of the work. Pedalling rates per metre covered might increase but the power needed to turn the pedal cranks should remain more or less constant on inclines if gears are used properly.