Trek Belt-Driven Bicycles Rely on Carbon Fiber Technology
You might expect to find high modulus carbon fiber in a bicycle frame—but in a belt drive system?
Based in Wisconsin, Trek builds bicycles designed to change people’s lives through cycling. Their Advanced Concepts Group (ACG) leads the way in advancing bicycle design and technology.
One of Trek’s lines is called the Urban Series. Including the District and Soho models, these bikes are made for the progressive urban market. They feature Gates Carbon Drive™ belt system—replacing the traditional chain drive found on the everyday bicycle. According to Michael Leighton, Senior Industrial Designer at Trek, “The Urban line is a collection of single speed and internally geared bikes that get the job done.” But getting the job done took a bit of doing.
A big part of designing the single-speed, belt-driven bike fell to Ray Waxham, R&D Engineering/Team Projects, part of ACG. “The first (non-Gates) belts we tried didn’t work,” said Waxham. “We applied them to one of our early designs, and after weeks of machining and getting all the parts together, the first time I put my feet on the pedals the belt just spun.” It was back to square one. Trek then tried some imported belts, but they didn’t work out either.
“I had heard about Gates belts on motorcycles,” Waxham said. “If they can work on a motorcycle, they can work on a bike.” So began the dialog between Gates and Trek.
Waxham ordered Gates Carbon Drive System for testing. With the carbon fiber reinforced belts in hand, the challenge was engineering the frame. In a belt drive system, the bike’s rear frame triangle must be “split” to allow the belt to be installed. But splitting the rear frame triangle creates a challenge in achieving proper frame stiffness.
Trek experimented with various tube/frame designs, using Finite Element Analysis (FEA) data to compare the results. They used the data to create a new frame tube that had the required stiffness but without the bulk.
Although a Carbon Drive belt only weighs about 80g, much less than the standard chain, Trek tested varying belt widths in order to reduce bike weight as much as possible. Ultimately a 10mm wide belt satisfied the design requirements. No changes were needed in the belt’s construction except cosmetic ones to match the overall “look” of the bike.
Sprocket wear posed another challenge. Initially, Trek tried anodized aluminum sprockets. The sprockets were tested on a prototype bike that was ridden in several single cross racing events. Trek found that the contact points between the belt and the sprocket had worn. That led to a consultation with Gates engineers, who recommended a proprietary flame spray coating called Armour-GK™. This coating improves sprocket wear resistance and durability to the point where the sprockets are unlikely to wear out in the life of a typical bike.
Trek dealers began receiving production models of the Soho and District belt-driven bikes in mid-2009. The bikes are pre-sold when they reach the shop, and the orders keep coming in. Urban bike enthusiasts like them because the belt drive system is clean (no grease to soil clothing), whisper-quiet and requires no maintenance. Trek will soon introduce a Gates Carbon Drive for their top end commuter bike.
What can Gates do for you? For help with your application, speak with a Gates product application engineer at 303-744-5800, or email firstname.lastname@example.org.
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