Framing Carbon Fiber

The material gives cyclists a competitive edge – So why are designers spinning their wheels?

( I.D. magazine, May 2004)

When Mike Burrows strolls the fair-grounds of the big international bicycle-shows in Las Vegas, Friedrichshafen, Germany or Milan these days, he has a hard time shaking off a certain disdain for what is on display. In the past two years, bicycle manufacturers have taken to making everything imaginable out of carbon fiber – from frames and frame parts to components such as wheels, headsets, seat-posts and even chain-rings.

Mike Burrows was a pioneer of building carbon fiber bicycles in the 1980s and his design of the "Lotus" bicycle frame, that won Britains Chris Boardman a gold medal in world record time at the 1992 Olympics, is considered ground-breaking and iconic. It radically departed from the diamond shape of conventional bicycles – it was organic rather than geometrical, a solid body rather than an assembly of straight tubes. Burrows continues to advocate carbon as the "best material structurally" to build bicycles with. However, these days, Burrows finds the precious black stuff is frequently being molded into "catastrophic" shapes, as he calls them. Carbon fiber, Burrows finds, should not be used unless it structurally makes sense. And a lot of the current use, according to Burrows, bears "no logic whatsoever."

Burrows, a former competitive cyclist from London and author of the seminal book "Bicycle Design", hand-built his first carbon fiber bicycle in 1983, for his own use in a race. Carbon fiber had first been discovered by the aero-space industry as a material with extraordinary qualities – no other material offered the same stiffness and structural stability at such a low weight. By the 1980s it was also widely used in car-, boat- and motorcycle-racing and Burrows was eager to put the qualities of the fiber to use for his own sport. Soon Burrows discovered, that the material had the potential to revolutionize the very concept of what a bicycle is. For more than 100 years, bicycles had been welded-together tubes – of steel or, more recently, aluminum, which was dicovered as a new matertial to make bicycles from at about the same time that carbon fiber was. But unlike the two metals, carbon fiber can be molded into any shape the designer would like to mold it into. The days of the classic double-diamond shape of the bicycle seemed to be numbered. Henceforth there was no more limit to the desingers imagination in connecting the four points functionally defining a bicycle – steerer column, bottom bracket, seat-post outlet, rear drop outs.

Designers, who, like Burrows, understand the opportunity and the challenge that carbon fiber poses to bicycle design, agree with him in criticizing the current trend. Stefan Behrens, a German aerospace engineer and a cycling aficionado who uses the resources of his employer FEM – a builder of satelites - to produce a very advanced carbon-fiber bicycle-frame, finds the trend "alarming". The market, Behrens says, demands the carbon fiber- look and - feel for its high-tech cachet. As a result, "manufacturers who have no experience with carbon fiber are fooling around with it." The result are bicycles and parts that are at times technically far inferior to what could be made of aluminum, titanium and steel. In some cases dangerously so: seatposts and headsets (the fixture holding the handle bars) of carbon-fiber have been known to break easily, while the rider is traveling at up to 30 miles an hour. "A lot of the carbon fiber on the market now is candy and jewlery. It is not always the best decision," says Brad O'Hare, designer at Softride – a company known for its intrguing use of a carbon fiber beam on an aluminum frame to improve cycling comfort.

Part of the problem is that what's considered by purists - such as Burrows, Behrens or the Swiss designers Rudi Kurth and Andreas Walser, - to be the proper use of carbon fiber has been made all but impossible in the construction of road bikes by the UCI (Union Cycliste Internationale), the governing body of world cycling,. In 1999 the UCI – whom Mike Burrows likens to the "Spanish Inquisition" – banned all shapes but the classic diamond from racing. This does not prohibit designers from building progressive bicycle shapes but it has made it extremely hard to market them. Road cyclists tend to want the bicycles that the stars of the sport use – so if the champions aren't using advanced shapes, the bikes won't sell on a mass market. Andreas Walser, a former architect, who hand builds carbon fiber bicycles for some of the best racers in the world, used to build a shape not unlike the Lotus. "Since 2000," he complains, "I have not sold a single one." On the other hand he has had a greater demand than he can satisfy for the diamond-shape bicycle, that he now builds for the German pro and Tour de France runner-up Jan Ullrich.

Trek, the Wisconsin based company that builds Lance Armstrongs bicycle, thoroughly exploits this desire of the average rider to sit on the same bike as the stars. The very diamond-shape carbon fiber bicycle that Trek builds for Armstrong every year, is available in stores only weeks after Armstrong can be seen winning the Tour with it on TV. The OCLV (Optimal Compaction Low Void) and its successor, the "Madone" are by all standards excellent bicycles but Walser, who builds for Armstrongs rivals, thinks they really don't need to be made from carbon fiber. "You can build a bicycle with the same qualities from aluminum", Walser says. "The frame of the Trek is assembled from 11 parts that are stuck into each other and glued. It can't be the goal to make a bicycle frame out of as many modules as possible!" Carbon fiber offers the oportunity to make a bicycle in one piece out of a single mold – a so called monocoque. An opportunity that according to purists such as Walser should not be missed. Trek built an interesting monocoque until 2000 – the Y-Foil. The Y-shaped bicycle provided suspension for the rider and hence relief for the cyclists stressed back. But while it was a highly acclaimed design, Trek stopped production after the UCI ruling.

These days the production of moncoques is no longer economically viable. One mold, according to Stefan Behrens, costs approximately 25.000 Dollars to produce. For four frame sizes that would mean spending 100.000 Dollars: "You don't have to be a business man to figure out, that that doesn't make sense, if you are going to sell no more than 100 bikes," Behrens says. Which are approximately the sales to be expected since the UCI ruling.- Rudi Kurth, the Swiss designer of the Cheetah, known for its intriguing integration of handlebar and fork into one piece, has sold exactly 130 bicycles since first building it in 1996. "My clients these days are triathletes, that don't have to conform to UCI rules, middle aged men with back problems and a lot of money and a few design lovers", says Kurth, whose bicycles sell for 8.500 Swiss Franks or approximately 5.600 Dollars.

But despite these economic constraints, carbon-fiber purists have not given up their quest for the ideal bicycle shape. Although they are not sure, whether there is an ideal shape. Andreas Walser says, that the shape of the Lotus, that is not very different from his no longer selling non-diamond monocoque "Modell 1" or Kurths Cheetah, is ideal, if you are emphasizing aerodynamics. If however, one puts riding-comfort into the mix of desired qualities, shapes become as varied as Softrides beam-design or Kestrels pioneering "Airfoil", which omits the seat-tube. "There is no ideal frame design, because there are so many variables in what's needed," says Preston Sandusky, Product-Director at the Santa Cruz based Kestrel. The diamond shape, Sandusky adds, is probably not the ideal shape, but a good starting point. This starting point has defined what a bicycle is for over 100 years. Carbon fiber has allowed a remarkable break from this starting point and allowed for the creation of a mutlitude of shapes. It would be a shame if the journey would end so soon after it started.

Sidebar One: Real or Virtual – Computer-Design versus Intuition

"Michael is my test-lab," says Andreas Walser, a trained architect from Switzerland who is considered by his peers as the 'artist' among carbon-fiber bicycle designers. Michael is Michael Rich of Germany, Olympic champion and two-time silver medalist in the pro world-championship individual time trial. Rich weighs a sturdy 180 pounds and is the master and commander over two truely frightening thighs. Rich has worked closely with Walser in designing bicycles ever since Walser making carbon fibre bikes a good ten years ago. "If my bikes can withstand Michael", says Walser, "they can withstand anything."

Michael Sagan, a trained industrial designer who designs bicycles for the Wisconsin based company Trek, takes a different approach. To make his bicycles as light and aerodynamic as possible, while not compromising their stability, Trek uses sophisticated computer software that calculates the forces which may impact a given design. 3D virtual prototypes are used to test the functionality of the designs before the expensive molds for the parts of the new frames are produced.

Walser is skeptical of such procedure: "No software can predict what happens inside a frame if a guy like Michael goes over a pothole at 40 mph." Which is why his designs derive from trial and error and the feedback he gets from one of the strongest riders in the world. This information tells him, where on the bicycle to add another layer of carbon fiber sheets and where to ommit one.

World class racers trust Walser – many of the best riders buy his hand-made bikes and paint them with the finish of their respective sponsors. Including Lance Armstrongs toughest challenger, the German Jan Ullrich. However, Walsers greatest triumph was not when Jan Ullrich won the first individual time trial at last years Tour de France against Lance Armstrong. It was when a high ranked employee of Trek-Europe bought one of his bicycles last year. "He said he bought it for a racer who is a friend of his. I think I know the name of that racer – Lance Armstrong." Trek seems to be taking a good look at "the Walser." "No one handles carbon fiber like Walser," says his colleague, bicycle designer and aerospace-engineer Stefan Behrens admiringly. Can such actual physical trials and gifted craftsmanship be replaced by computer simulation? The engineers and designers in Wisconsin would sure like to find out.

Sidebar Two: The art of making a monococque

Carbon - the raw material of carbon fiber bicycles – comes in wallpaper like sheets. A true moncoques – carbon fiber bike frame produced from a single mold - is produced by laying out the sheets into a pre produced mold. The production of the molds is very expensive and makes monocoque bicycles so pricy. The inside of the shapes is usually filled with a ballon, foam or epoxy. Then the mold is closed and the frame is "baked" at high temperatures. Often the balloon remains inside the bicycle.

The trick in laying out the sheets into the mold is that carbon fiber is stiff and stable only in the direction of the fibers. To achive the desired stiffness and strength at the most stressed points of the frame such as the bottom bracket requires a great deal of sophistication and experience in handling the material.

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