Getting into gear: Unraveling the mysteries of bicycle gearing

Why do bikes have so many gears? Even high-performance cars can usually manage with five or six, so why do some bikes have as many as thirty? And if it’s really necessary to have that many gears, why do some of the fastest bikes in the world have only one?

There is one simple reason to have gears on a bike – to make pedalling easier or more efficient. This can express itself in several ways – going faster for the same effort, going at the same speed for less effort, or being able to ride up a hill that would otherwise force you to walk. The more gears available, the easier it is to maintain the optimal pedalling rate or cadence.

Early bikes made do without gears at all and the history of the development of gears is fascinating in itself, but the vast majority of modern bikes have gears. Internal gears in the rear wheel hub are widespread, especially on utility bikes, and gearbox systems are starting to make an appearance on some mountain bikes, but derailleur gears remain dominant on most road, touring and mountain bikes.

Derailleur gears may look complex, but that’s mostly because all the works are exposed; mechanically they are really very simple. Nevertheless, making the best use of derailleur gears does demand a modicum of skill, though this is not hard to acquire.

The mathematical niceties of gear ratios may appear quite esoteric, but they can come in useful when comparing different bikes, for example if contemplating a hilly ride or tour and wanting to know which bike will tackle the steep grades more easily.

In all this talk of twenty or thirty gears, there’s something quite refreshing about the sheer simplicity of a single-geared bike. Track bikes have a single fixed gear. The banked track of a velodrome, where a skid can turn into a steep slide, makes brakes dangerous, so the fixed wheel allows safer deceleration.

Of course there are no hills or headwinds so there’s less need for gears for that reason. It’s also true that many track events run off within a fairly narrow speed range so there’s no need for variable gears – as long as the bike is set up initially with the right ratio.

Single-speed bikes are also favoured by a select band of enthusiasts for their lightness and simplicity. Some swear by them for mountain-biking in winter as they are much easier to clean and maintain. Some roadies use them for winter training too, as a low single gear obliges the rider to develop a fast, supple cadence.

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