Belt-Driven Bicycles: New Standard or Just a Fad?
A belt-driven bicycle: itâs the next best thing. The progression of two-wheeled technology has brought many ânext best thingsâ in all shapes and sizes. Remember GripShift and V-Brakes? A belt-driven bicycle doesnât have a
chain; at least not the one you might be picturing at the moment. Instead, a belt-drive (also known as a chainless bike or a poly chain) is actually one continuous piece of reinforced rubber that acts just like a standard roller chain. Itâs relatively flat on the outside and has molded teeth on the inside. In essence, its design is very similar to that of a timing belt found in certain automobiles.
Perhaps one of the most curious aspects of the belt-drive system is the configuration of the poly chain with the
frame of the bicycle itself. If you think about it, a typical roller chain can be disconnected to be threaded through the chainring and cogs before being reconnected. A belt, on the other hand, is a continuous piece of material that would be useless if broken. For chainless bicycles, the solution is a frame designed with a space (slot) at the junction of the seatstay and chainstay on the drive-side rear drop-out. During installation, the poly chain is pulled through this gap and then stretched around the
drivetrain components. Once the belt is fit and tensioned, the gap is reinforced with a special bracket that bolts to the inner and outer sides of the drop-out. Although this split has the potential to compromise frame stiffness, manufacturers anticipated this deficiency and have compensated with innovative tube and frame designs.
Despite the recent trend of bicycles using this technology, the cycling community still seems to be divided on the topic of belt-drive systems. And rightfully so, a chainless bike has just as many positive aspects as it does drawbacks.
Pros - Although some hard-core cyclists may consider belt-drives a little gimmicky, they do have some obvious and surprising advantages.
Low Maintenance: Belt-drives require no lubrication. This makes them great for the serious commuter â no more worries about greasy pant legs.
Weight: Belt-drives are lightweight; a poly chain weighs right around 55-grams. Compare that to a typical chain that can tip the scales at 300-grams or more.
Strength: Reinforced with synthetic threads like carbon or Kevlar, recent designs have higher yield strength (break strength). This means that itâs easier to break a traditional roller chain than a poly chain.
Long Lasting and Economical: Poly chains have a longer life span than their roller counterparts, lasting somewhere in the neighborhood of 8,000- to 10,000-miles. This is significant for the hard-core, penny-wise cyclist.
Power/Efficiency: It has been said that pedaling power and efficiency can be lost when using a poly chain. Interestingly, there was a study released at the 2009 Interbike that revealed no loss in pedaling power and efficiency when comparing a traditional chain drive set-up to a belt-drive system.
Cons - Although belt-drives have the potential to be the ânext big thingâ, they are still specialized and work for only a select group of bicycle configurations.
One-Dimensional: Currently, itâs only possible to run a belt-drive system with a
singlespeed or internal gear hub bicycle; derailleur systems are still in the research and development phase.
Specialized Components: Belt-drives require purpose-built components in order to wear properly. The most recent designs are either finished with a unique proprietary, skin-line coating or are manufactured with composite materials. This is necessary to counteract the wear than can occur between the contact points of the belt and the chainring/cog.
Climate Control: Weather can also be a factor with chainless bikes. I recently got some feedback from a colleague who is a dedicated commuter. She lives in Colorado and commutes year-round. One particular day, when the temperature plummeted into single digits, she ended up walking her bike home. Her poly chain had âfrozen upâ, losing most of its flexibility and managed to become totally ineffective.
Wherever you stand, chainless bicycles are most likely here to stay. The subtle nuances of belt-drive systems will most likely iron themselves out as the technology is refined and the concept is more widely accepted.