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WINTER 2007-08


Letter from the Editor


Student Profile: Daniela Cadore

By Michaela McBride

Student Profile: Erin Hammons

By Ashley Johnson

Tech Guru

By Brian Neilson

Mechanism Improves Cyclist's Performance

By Khoa Chu

Alumni Tips

By Hannah Peterson

Bridges: Two Cities, Two Perspectives

By Brian Nielson

Bike Lanes: Making Space for Safety

By Natasha Richardson

Engineering the Downhill Bike

By Matt Buxton

Alumni Tips: Mindy Yechout

By Hannah Peterson

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Engineering the Downhill Bike

As in other sports, the engineering of highperformance bikes draws large budgets and a great amount
of time. This is especially true in competitive downhill racing where athletes are always looking for an edge over their opponents. The competition has kept engineers working constantly to produce faster and stronger products in order for their companies to remain viable.

Tomac Mountain Bikes, a company based in Lincoln, Neb., produces high-performance bikes. Tomac recently designed a high-performance downhill bike intended for competitive use. The Primer 220 DH will be the third addition to the company’s current line that includes a cross-country bike and a mountain bike.

Tomac bike

Joel Smith, owner of Tomac, commented on what makes Tomac different from large companies.

“The main (difference) is the direct involvement we have with all aspects of bikes development,” Smith said.

The members of Tomac are experienced riders and many have competed on the international level. From the start to the finish of development, their experience and high level of involvement ensures that they create a product that will be able to perform well in competition.

The Primer, which is in the final stages of design, is an update to Tomac’s older Magnum 204 downhill bike. The staff liked the Magnum for its suspension characteristics and wanted to optimize those properties in a new
bike. Unlike larger companies, Tomac started designing the Primer 220 from scratch.

The Primer 220 “is designed for a very specific and unique application: big jumps, drop offs and generally extremely rough terrain. In fact, the end user is typically riding a chair lift to access the trails, so it’s not your normal Sunday afternoon ride around town bike,” Smith said.

Simply put, downhill biking is a race to the bottom of a steep hill. And while skill is a major factor in handling the terrain, the race is a short one – meaning the performance of the bike is extremely important.

A major consideration in performace is weight of the frame. The Primer’s frame is built out of aluminum alloy tubing. They used both aluminum 6061 and 7005. Aluminum 7005 has higher yield strength than Aluminum 6061, so it is used for the largest components of the bike, including the swing arm of the rear suspension and the front triangle. While Aluminum 6061 has lower yield strength, it is easier to machine, so the parts that require larger amounts of machining are made from Aluminum 6061.

bike chain

During design, the Primer would go from design on a computer to testing of a physical prototype and back to design until they found an ideal build. During some points of testing they experienced problems that were unexpected.

One problem they found was with the Primer’s suspension.

Mark Landsaat, an engineer who worked on the Primer 220, said, “We are trying to achieve maximum travel in a package that is as compact as we can make it. This automatically results in some very tight tolerances between all the moving parts.”

The Primer 220’s suspension has an extremely large range of motion. This range of motion, or travel, allows the rider to handle greater obstacles while maintaining high speeds. Most bikes have about 80 millimeters of travel while the Primer has about 200 millimeters of travel.

While testing a prototype, they found that the resistance in the rear suspension would deteriorate at an exponential rate. This means that the suspension offered normal resistance to a certain point, at which the suspension would begin to compress more and more quickly.

The amount of force to compress the suspension 1 millimeter when completely uncompressed was greater than the force to compress the suspension the same amount when the bike was closer to being fully compressed. Essentially this meant that the bike was bottoming out, which results in a rough and unmanageable ride that could possibly damage to the frame.

The levels that the Primer was bottoming out at were beyond

the range of basic riding. But because the members of Tomac had the skill to push the Primer to levels where it would bottom out, they were able to identify and solve the problem.

The Primer 220 DH is now close to being finalized and is in production with planned release in 2008. It is the most complex bike that Tomac has produced and has been received well by those have tested it.

The level of attention that a small company like Tomac can offer to the process of development allows them to develop the most competitive product that they can deliver. And in competitive sports, it is absolutely essential that a company delievers the most competitive product to the athletes.

“Especially in downhill racing, where typically you’re talking hundredths of a second,” Landsaat said, “the performance of the bike can be the difference between being on top of the podium and not being on the podium at all.”



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