Columbus, OH USA
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Pedal Pusher
November 2008
by Greg Knepp
greg_knepp@email.com
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See Letters to Greg KneppGears 101
Illustration by Greg Knepp
The first question I get from your typical novice cyclist looking to buy a bicycle is usually about gearing: “Why do I need all those gears?” The question is often asked with a degree of consternation. And for good reason; if a machine as hugely complex as an automobile can get along on four forward gears, why would a simple device like a bicycle need four or five times that number, particularly in light of the fact that some bikes are marketed having only a single speed?
The answer is simple: an automobile has a gasoline engine capable of generating an enormous amount of energy. Hence, the automobile (at least up until now) hasn’t needed to be particularly efficient on a mechanical level, due to its greater energy reserve. You, on the other hand, have a set of legs. Your ability to “step on the gas” for more speed or to power up a hill is severely limited because your legs are the sole energy source for your vehicle. Multiple gearing helps even out the expenditure of your energy in a way that is simply more efficient. This is particularly important on long rides or on rides where hilly terrain, challenging road surfaces or adverse wind conditions are factors.
At the risk of boring you with cycle-babble I’ll elaborate: It has been determined that a pedaling cadence of approximately 96 full revolutions per minute against light to moderate resistance is ideal for most cyclists. For a variety of reasons, this rate may vary somewhat during a ride, as well as from rider to rider; still, 96 RPMs will facilitate an effective use of pedaling energy over the long haul, while ensuring maximum bicycle control. This cadence seems to be natural to the body; you needn’t time yourself while counting pedal strokes. The body will want to achieve this rhythm (or something near to it) on its own. Faster pedaling compromises balance while slower compromises strength as well as muscle, ligament and tendon health.
How can a rider maintain this RPM-resistance relationship under varying road conditions? Simple, by changing gears and changing them often. Pedaling up a steep hill in the lowest gear (called the ‘granny gear’) will be slow going, but the pedal cadence and resistance should be about the same as the cadence and resistance associated with speeding along a straightaway under a stiff tailwind in the highest gear. The idea is to allow the speed of the bicycle to vary while maintaining a more or less constant energy output. Distance tourers and serious commuters have bikes with lots of gear selections and wide ratio ranges, and they use them! Serious cyclists change gears so often that it becomes automatic – even unconscious.Question: I see a number of single speed bikes around. Are they of no value at all?
Answer: Well, they’re good for exercise. Single-speed bicycles (both fixed gear and free-wheel versions) have made a comeback among young cyclists, but this phenomenon represents an odd counter-cultural trend that, while laudable in a certain hip-minimalist way, is not necessarily appropriate for the typical cyclist. Similarly, fat-tire retro bikes have been popular for some time now, and are usually marketed in “authentic” single-speed versions. But some also come with six-speed derailleur options at an extra cost. My advice: damn the authenticity and get the derailleur version! You’ll thank me on your first trip up the hill from Buttles and Neil to High Street.Question: Some multi-geared bikes have strange looking mechanisms hanging off the rear wheel hub while others don’t. What gives?
Answer: There are two gear systems used on bicycles, both invented about a century ago and both honed over the decades to a high degree of technical sophistication. The most popular is the derailleur system. This system is characterized by a configuration of progressively sized chain rings mounted at the hub of the rear wheel. The chain moves by being shifted, or literally derailed, off one cogged ring only to land on another ring of a different diameter, thereby changing the travel ratio of the power source to the rear wheel. Most derailleur-equipped bikes also have a separate front derailleur system which shifts the chain on the crank (pedal) wheel as well. The rear chain ring cluster will have from five to nine separate rings, while the front (or crank) cluster will have three. Each system is controlled by its own set of handlebar-mounted shifters. A 21-speed bike will have three chain rings on the crank and seven on the rear hub. Theoretically this will yield 21 possible gear combinations. In reality though, at least two of the combinations are unusable due to diagonal stress on the chain, and the outer rings on the crank chain are only used at the speed extremes (very slow and very fast). The result is that most cyclist will stick to about six or seven reliable combinations. This may still seem like a large number of gears, but such a wide selection allows for smooth, modest transitions from one gear to the next – easy on the bike and easy on the legs. In fact, a cyclist is seldom aware of exactly which gear he’s in. He simply changes gears to arrive at a maximum level of leg comfort and forward progress.
The other gear option is the in-hub system, and it is very different from the derailleur system in that it is a more conventional (though complicated) gear arrangement, much like an automobile transmission. The handlebar-mounted gear shifter operates a set of tiny cog wheels enclosed within an oversized rear hub. These cogs are pulled into various combinations, thereby changing the relationship of the outer hub (which is directly connected to the wheel via the spokes) to the inner axle. Three-speed and five-speed bikes are almost always equipped with in-hub systems. Seven and nine-speed in-hubs are also available.Question: Which gear system is better?
Answer: Touring, off-road and racing bikes are universally equipped with derailleur systems. Hybrids and some town and commuter bikes are also derailleur equipped, but an increasing number of the later models are in-hub equipped. Recent improvements in in-hub technology, allowing for greater reliability and increased gear selection, have fueled a resurgence of the popularity of such gearing, particularly on bicycles intended for local rather that long-distance use. The in-hub system has the advantage of being fully enclosed. The need for routine cleaning and maintenance is largely eliminated. In-hubs are inconspicuous and allow for full chain-guard protection. Conversely, combination crank and rear derailleur systems preclude chain guards entirely. There are distinct disadvantages to in-hub gearing, however: they can be noisy and they produce their own mechanical drag. Derailleur gears, by contrast, are uniquely free flowing and rather simple on a mechanical level. Derailleur gears also incorporate a spring-loaded chain tightening function. Chain slackening is a nuisance universal to single-speed and in-hub equipped bicycles.
I personally prefer the derailleur system. Both of my road bikes as well as my tandem are derailleur equipped. But I have an Electra Townie equipped with a Nexus in-hub three-speed system, and I’m very happy with it.
Remember, if a wide selection of gears intimidates you, simply leave your bike in a comfortable gear and never touch the gear changers again – instant single-speed bike! But converting a single-speed into a multi-geared bicycle will cost at least $150.00. Take your choice, and happy wheeling!Greg Knepp is a Short North cyclist
greg_knepp@email.com© 2008 Short North Gazette, Columbus, Ohio. all rights reserved
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