Archive for April, 2012

What Length of Belt Should My Bike Wear?

A lot of well-dressed bicycles are wearing belts these days.  They make a clean, crisp fashion statement on the runway, the road and the bike path.  Unlike a chain (or the belt on your pants), though, the length of a bike’s drive belt can’t be adjusted.  The length of the belt depends on the size of the front and rear sprockets, and the distance between them.

Gates Carbon Drive Belt Drive Belt Length CalculatorSo how does the well-heeled bicycle owner decide what is the right belt length for his or her bike?  Fortunately, our friends at Gates have created a handy belt length calculator.  It’s an easy to use Excel spreadsheet you can download to your computer.  You can find it here. Once you arrive at the Tech Info Page, select “Belt and Sprocket Size Calculator” under the heading “Technical Manual.”  (Skip the Carbon Drive Systems Calculator also appearing on that page – it’s not nearly as useful.)

If you are setting up a single speed, calculate which combination of front and rear sprockets will give the ratio you want.  In general, a smaller front sprocket will give better clearance with the chainstay.

For internal gear hubs, consult the manufacturer’s data on ratios.  Select a combination of front and rear sprockets so that you will have the low gear you want.

Make sure your combination of sprockets and belt length work for your bike’s chainstay length.  The calculator will give you the required range of adjustment to take up belt slack.

With the right belt length, your bike will be well-appointed and give you years of carefree riding.

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News Flash: Belts Are Now As Efficient As Chains!

The diamond-framed “safety” bicycle replaced the high-wheeled “ordinary” by the end of the 1800s.  Apart from a few shaft-driven bikes, chains have ruled since those early days.  Although belts have been used to transmit power since at least the 1870s, when flat leather belts linked steam engines to farm equipment and industrial machines, it’s taken over 100 years since then for belts to be successfully adapted to bikes.  The reason has to do with efficiency.

The human engine doesn’t develop much power, and when we jump on a bike, we want our pedaling effort to translate into maximum forward motion.  Until the development of modern cogged belts, nothing could compete with the transmission efficiency of roller chains.

Often called timing belts or synchronous belts, cogged belts are popular in applications that require precision, durability and efficiency.  Many cars use a timing belt to drive the camshafts that control the opening and closing of the engine’s valves.  In 1962, the German Glas 1004 became the first mass-produced vehicle to use a cogged timing belt in place of a chain.

CenterTrack on the OUR Blue Speedhound

CenterTrack on the OUR Blue Speedhound

Our two-wheeled friends in the motorcycle world are also fans of cogged belts.  In 1980, Harley-Davidson introduced a Gates Kevlar reinforced belt as a replacement for its chain drives.  That year, they debuted the FXB Sturgis model featuring the belt drive in honor of the iconic motorcycle rally.  Other motorcycles, including BMW and Victory, use final drive belts.  Snowmobiles are almost all driven by belt transmissions.

In about 1985, Bridgestone introduced a belt-drive folding bike for the Japanese market.  The STRiDA folding bike was designed around the same time and also uses a cogged belt drive.  But despite all this cogged belt history, high performance belt drive for bikes only became available in 1997, with the Gates Carbon Drive system.  http://www.carbondrivesystems.com

According the U.S. Department of Energy, cogged belts are about 98% efficient.  http://www1.eere.energy.gov/manufacturing/tech_deployment/pdfs/replace_vbelts_motor_systemts5.pdf This means that 2% of the input power is lost, which is about the same efficiency as a roller chain.   Kidd, Matt D.; N. E. Loch, R. L. Reuben (1998). “Bicycle Chain Efficiency”. The Engineering of Sport conference. Heriot Watt University.

Belt drives have been used for decades to drive vehicles much heavier and more powerful than Speedhounds.  Now that belt technology has finally caught up with bicycles, we think belts are a perfect choice for getting you up those hills and through the rain and snow you might encounter on your rides.

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