Issue: Volume: 23 Issue: 12 (December 2000)

Designer Cycles

For children, the biggest issues concerning the design of a bike are its color and whether it includes the "must-have" accessories. For adults, the main concerns are more diverse, especially among competitive riders. For them, performance, comfort, and style are all key, and they are willing to pay a premium price for these features. That's why high-end bicycle manufacturers are willing to go the distance when it comes to designing racing bikes.

Consider the examples of racing bike makers Trek Bicycle and Kestrel USA. Both used advanced computer-aided design and surfacing software to create their newest racing models. But while their tools and techniques were similar, their design objectives were significantly different.

Trek focused on creating the fastest possible model for a particular rider-Lance Armstrong, bronze medalist and two-time winner of the Tour de France. Moreover, the design had to adhere to the rigid specifications dictated by the governing body for international racing, which apply to most of the events in which Armstrong competes.

By contrast, Kestrel's bike was created to appeal to triathlon racers in general, so aesthetics and aerodynamics were of equal concern in the design process. To entice customers, the bike had to look as fast as it performed. And it had to meet a different set of specifications that governs triathlon events.

The following articles tell the story of bicycles built for two: two sets of design criteria for two types of customers. They also describe how Trek and Kestrel met their objectives and delivered sleek, aerodynamic products in record-setting time, proving the flexibility of digital design and making computer-aided design tools and processes the clear winners in this quest.

-Karen Moltenbrey

Trek's digital design proves itself a winner
By David Cohn

Bicycle racing isn't exactly considered a big-league sport in the US. But Lance Armstrong's stunning repeat victory at the Tour de France this past summer and his bronze-medal performance in the 2000 Olympic time-trial cycling event has generated interest in the sport and a new following of fans. At both events, America's reigning cycling champion has peddled his way to victory on a new high-tech creation from the Advanced Concept Group (ACG) at Trek Bicycle Corp. (Waterloo, WI), designed using a combination of the latest MCAD and industrial-design software.

The Tour de France, the world's premier bicycle race, is a grueling 2200-mile, 23-day survival test, conducted as a series of separate races called stages. With each day there is a new, different stage-one day may entail a flat road course, another a long climb over the Pyrenees Mountains. For this year's race, Trek supplied Armstrong and his US Postal Service teammates with three different bikes: one for flat road stages, a lighter frame for the mountainous sections, and a third for the race's three time-trial stages. While the road bikes were based on some of the company's existing carbon-fiber frames, Trek pulled out all the stops to design a new time-trial bike.

In time-trial racing, a rider races against the clock, going as fast as possible. When the very best cyclists in the world compete in such an event, fractions of a second make a big difference. Armstrong's 1999 time-trial bicycle was a titanium frame made by Lightspeed, but for the 2000 racing season, the entire team's bikes were supplied by Trek. The task for Trek was to design a bike with the ideal aerodynamic shape.

In August 1999, just a month after Armstrong's first Tour de France win, ACG lead engineer Doug Cusack, himself a top amateur cyclist, took up the challenge. His goal: To lead a secret "underground" team within the company to create a molded carbon-fiber time-trial bike to add to Armstrong's defensive arsenal for the 2000 Tour de France. Other team members would ride Trek's welded aluminum-frame time-trial bike.
Trek Bicycle and its premier user, Lance Armstrong, traveled the path from conceptual design to glory using 3D CAD tools and surfacing software. (Photo by Graham Watson. Conceptual art by Trek Bicycle.)

Cusack began by taking coordinate measurements from Armstrong's 1999 bike to analyze the geometry of its titanium frame. Once Cusack reproduced the centerlines of its tubes in CADKey (Marlborough, MA) CADKey software, he imported the drawing into PTC's (Waltham, MA) Pro/Engineer, where he began to lay out aerodynamic tubing shapes, based on past studies originally done for the design of fighter jet wing struts. Cusack's aerodynamic shapes not only had to reduce drag, but also had to fall within the envelope for allowable bicycle design as specified by the Union Cycliste Internationale (UCI), the governing body for international cycling.

In September, Cusack and renowned wind-tunnel cycle coach John Cobb traveled to Texas A&M University, where they met with Armstrong, who brought his 1999 time-trial bike for a battery of wind-tunnel testing. Cusack and Cobb also brought a Trek aluminum-welded frame, to which Cusack had added clay mock-ups of his new aerodynamic design. Armed with the results of the wind-tunnel tests, Cusack returned to Wisconsin, where he enlisted the aid of ACG industrial designer Michael Sagan to create the concepts, shapes, and aerodynamic surfaces for the new cycle. Working with Trek engineering carbon-fiber expert Jim Colegrove, Sagan brought the Pro/E data into Alias|Wavefront's (Toronto) Studio Tools running under Windows NT on Pentium-based workstations from SGI, where he began developing sketches and surfaces for the new frame.

One month later, using Sagan's Studio Tools files, model makers Paul Andrews, Paul Towne, and Jarod Brown used Surfware's (Westlake Village, CA) SurfCAM to fabricate a full-size model of the new bike from a wood-like prototyping material.

Following more tests and feedback from Cobb and Armstrong, the group found that the new shape would save nearly 25 seconds in a 40 km time-trial event. (The Tour de France includes three time-trial stages of 16, 69, and 49 km. The Sydney Olympic Time Trial was a single 46.8 km race.) Cusack and Sagan also experimented with using a single-sided fork instead of a conventional two-bladed fork. While that design resulted in a 10 percent reduction in drag, it it didn't fall within the accepted UCI guidelines, so it couldn't be used.
Trek uncovered highly stressed regions in its original bike design using Structural Research & Analysis' Cosmos/Design-Star FEA software.

After a second round of wind-tunnel testing in November 1999, Cusack and Sagan used Studio Tools to modify their model and began looking for other areas where they could hone Armstrong's competitive edge. For example, in the Tour de France, riders often carry water with them during time-trial stages, not so much to remain hydrated during that day's race, but so they won't have a water deficit going into the following day's race. "We put a bladder inside the down tube on the bike and ran a hose up to the handlebars so Lance could drink while he was in the riding position," says Cusack. He estimates that the reduction in drag resulting from an external water bottle and the time saved by eliminating the need for Armstrong to get out of his tuck position to drink alone saved 15 seconds over 40 km.

Besides focusing on performance, the ACG team also began looking at the manufacturability of the bike. Originally conceived as a one-of-a-kind frame, Trek decided to sell the frame as a limited-production model, now available for $4500 for serious-minded riders. By December, with some modifications to increase the size of the tube cross-section and to recess the rear brake, Sagan released the Studio Tools surfaces for tooling. Rather than outsourcing this phase of the work to the company's regular vendor, ACG model makers brought the Studio files directly into SurfCAM and CNC Software's (Tolland, CT) MasterCAM. They then cut three of the six molding tools in-house, as well as all the aluminum hardware pieces such as dropouts (the points where the wheels attach to the frame) and seat clamps.

In February of this year, with the clock ticking, Sagan began working with Chad Bailey, Trek's graphic designer. After importing Bailey's flat Adobe Systems (San Jose, CA) Illustrator artwork into Studio Tools, Sagan accurately positioned the frame's decorative elements, ensuring that decals would properly wrap around the odd carbon-fiber tube shapes once they were manufactured.

In March, Trek's finite-element analysis expert, Chris Jones, used Structural Research & Analysis' (Los Angeles) Cosmos/ DesignStar software to run a battery of examinations on Sagan's Studio files. The results indicated changes were needed to improve stiffness in the drive-side dropout. Sagan made the alterations in Studio Tools, then exported the files back into SurfCAM, so the tools could be recut.

By April, Brian Shummann, Trek's composite frame engineer, had bonded the first of the unique carbon-fiber frames, and the paint and decals were applied. ACG mechanics assembled the bike, and Cusack made his first test ride. Then the bike was delivered to Armstrong in Europe, where he was training-several months ahead of the team's deadline. In May, after further development of the onboard hydration system and additional tweaks, Trek produced a similar frame for Postal Service team member Tyler Hamilton. Armstrong also received a new frame but ultimately rode the original version on which he trained.
Trek also used Studio Tools to accurately position decorative elements around the frame.

Finally, in June, Armstrong rode the bike to victory in the time-trial stage of the Dauphine Libre, the final season race prior to the 2000 Tour de France. Armstrong's victory in Stage 19 of the Tour de France, on his new Trek time-trial bike, proved to be the turning point in this year's race; after that win, his lead was so large that only a crash would have denied him his victory.

According to Sagan, development of the newly designed bike cost several hundred thousand dollars, but notes that figure would be several times higher without the use of Trek's array of software tools. The time savings were also significant. Sagan maintains that Trek would not have been able to produce the bike in time for the major 2000 cycling events, including the Olympics, using other methods. The company's normal timeline would have been approximately 15 months from concept to delivery. "We were able to cut the process in half because we could do the tooling in-house. We had all the modifications in one digital model, taking us from a concept to victory."
Designers used Studio Tools' diagnostic shading functions to evaluate the surface of the bike frame's bottom bracket.

Armstrong-whose name is now synonymous with cycling-has recently raised the awareness of bicycle racing in the American psyche. And digital design tools are helping Trek lead the pack in the race to capture the resulting market in his wake.

David Cohn is a computer consultant and technical writer based in Bellingham, Washington. He can be reached at

Kestrel uses digital design to make its bike as fast as it looks
By Karen Moltenbrey

The Ironman triathlon is a test of athletic prowess and endurance: a 26.4-mile marathon, a 2.4-mile swim, and a 112-mile bike ride. Only serious, well-conditioned athletes dare to compete in this type of race, relying solely on their own strength and ability for the swim and run. But for the cycling, their performance is also dependent on their choice of bike. It's for these athletes that Kestrel USA (Watsonville, CA) introduced its first digitally designed bicycle frame: the KM40 Airfoil, a lightweight, one-piece, carbon-fiber design incorporating low wind-resistance airfoils throughout its sleek form.

"The KM40 is well-suited for longer distances, where its aerodynamics and smooth ride have made it our most popular frame and one of the most popular Ironman racing bikes," says Preston San dusky, Kestrel's president and a "casual" competitive rider. "Its geometry is specifically tuned to the flat-back time-trial riding position, while the design's vertical compliance isolates the rider from bumps and road shock." The shape and size of the frame's tubes, however, prevent athletes from using the bike in certain international racing events such as the Olympics and the Tour de France.

For about 15 years, Kestrel had been designing high-end bike frames using traditional hand-modeling techniques, which were time-consuming and expensive. "We'd show a bike at a trade show, make the prototype the following year, then deliver the product the year after that," notes Kent Whiting, project engineer at Kestrel. To cut development time and costs, Kestrel last year teamed with product design firm IDE (Scotts Valley, CA) to create a new, stylized bike frame that was as aesthetically pleasing as it was aerodynamic. "To attract customers, the bike had to look fast and be fast," he says. By using digital techniques, the designers delivered on those requirements with a fine-tuned, mathematically precise product that conformed to specific racing regulations. And they did it in record time: from concept to delivery in the same year. "The key to a better performing bicycle is a better engineered bicycle frame," says Sandusky. "In racing, time is crucial, so any change, no matter how slight, can make a big difference at the finish line."
Through digital design, IDE created a perfectly symmetrical bike frame for enhanced aerodynamics, while shortening the development cycle for Kestrel, the bike manufacturer. (Images courtesy IDE.)

Adds Dave Moriconi, IDE president: "Modern triathletes need every advantage possible to help them perform to the best of their abilities. Our aim was to design a specialist bike frame utilizing state-of-the-art computer design and manufacturing techniques to give riders as much help as possible in their quest for a faster time."

Furthermore, the KM40 frame retails for about $2700; fully equipped, the bike can cost about $5000. So the athletes buying the frame are extremely discriminating. "In the auto industry, it's akin to buying a Porsche or Ferrari," says Moriconi.

Kestrel's bikes are easily identified by their one-piece airfoil frame. Because there are no joints in the finished frame, redundant material (and weight) for the connecting lugs, which can add almost a pound to the bike's total weight, is eliminated. However, for the team at IDE, whose previous digital design experience involved small consumer electronic devices, perfecting the geometric design for the KM40 proved particularly challenging even using CAD and NURBS tools.

"We typically work with a lot of smaller surfaces and use standard fillets, which have a constant radius cross section, or spline curve, for the entire length. But Kestrel's directive was that the frame had to be one continuous, flowing sculptural piece, which was difficult to achieve," says Doug Jones, senior design engineer at IDE. "It took a lot of rethinking on our part to accomplish progressive fillets, which vary in proportion over the entire length. And in the end, we had three major surfaces that had to be joined and blended together as one."

When the IDE designers began working on the project, their main objective was to create a complementary design for a bike created two years earlier using traditional techniques. But as the digital design progressed, the bikes be came less similar in appearance. "The aim was to continue the airfoil cross section that runs through the bike," says Andy Hooper, IDE industrial de sign manager. "But as the design evolved and more work was done to blend the surfaces, the frame began to look more elegant-as though sculpted by the wind."
Most of the KM40's design was accomplished in Rhino, where an IDE-customized workspace and macro commands made the process more efficient.

Adds Sandusky: "When you run your hand over the frame, you can feel that it changes shape and diameter continuously." To accomplish this unique shape, Jones began the design process by creating a skeleton of the frame in PTC's (Waltham, MA) Pro/Engineer running on a Windows NT platform. The seamless airfoil shape, however, negated using default CAD tools, with their built-in spherical and cylindrical forms. So after fashioning the bike's basic shape, Jones imported the data into Robert McNeel & Associates' (Seattle) Rhinoceros NURBS modeler, where he performed the majority of the design work-creating cross sections, lofting profiles, bounding curves, and surfacing networks.

"This single, full-blended form contained more complexity in terms of surfacing than anything we've ever done before," says Moriconi. "We spent about 30 percent of our time developing the primary surfaces of the bike and 70 percent modulating the surfaces, which shows how important the detail blending was. At times, Doug was literally smoothing the blends by adjusting the surfaces one node at a time."

To maximize the designers' control when manipulating and blending the complex frame geometry, Jones spent the past three years creating 750 macro commands and a customized workspace for working in Rhino. For instance, to accomplish incremental numeric node nudging, Jones developed approximately 150 script files that could be accessed through icons to perform specific functions that aid in the design process.

Once completed, the Rhino solids model was used to manufacture a full-scale CNC model for testing, evaluation, and assembly of the wheels, fork, and other bike components. Because the KM40 frame was based on a previous, well-analyzed design, it was not subject to rigorous finite-element analysis. The IDE team then made minor adjustments to the Rhino model based on the testing, and imported the NURBS model into Pro/E for direct tooling of the negative.

Designing a bike digitally was a first for Kestrel and IDE, requiring an investment by both firms. "When we started, we'd take two steps forward and one back," notes Moriconi,"though now, we're designing our fifth frame for Kestrel and have become more efficient." Kestrel's Whiting estimates that for the KM40, released a year ago, the company cut its development cycle by 25 percent. That time has since been reduced to 50 percent. "We can now conceptualize, design, and manufacture a bike all in the same year," he says.
The biggest challenge facing the designers was blending the network of Rhino NURBS surfaces, which make up the bike frame's complex airfoil design.

All told, the KM40 has become both a technical and a financial success. In trial testing, the design averaged a six-second reduction over the previous model. While the bike didn't net a win in this year's recent Hawaiian Ironman competition, it did receive a silver medal in the international 2000 Industrial Design Excellence Awards.

Karen Moltenbrey is a senior associate editor of Computer Graphics World.