I wouldn’t call myself a “serious” cyclist, since I don’t wear neon Spandex shorts and top, a colour-coordinated helmet, leather gloves or fancy cycling shoes. Heck, I don’t even have a water-bottle. But I do cycle a bit, and as I was puffing my way along the bike path the other day it seemed to me the time was ripe to write about the science of cycling. (Besides, I’m a sucker for alliteration.)
The first step in the development of the bicycle was the “celerifere,” or wooden horse, invented in France in the 1790s. It had a fixed front wheel, so it couldn’t be steered, and the rider propelled it by pushing his feet along the ground, a la The Flintstones.
A smart German baron, Karl von Drais, finally realized the machine would be a lot more fun if you could steer it, and added a steerable front wheel in 1817, creating the “draisienne,” or dandy horse. In 1839, Kirkpatrick Macmillan, a Scottish blacksmith, made a machine with pedals, which drove the rear wheel by means of cranks.
In the 1860s the French took the initiative again, inventing the velocipede, on which the pedals were attached directly to the front wheel, so that once around with the pedals meant once around with the wheel. That, in turn, meant that the larger the front wheel, the faster the bicycle. This led to the “pennyfarthing” bicycle, on which the front wheel, over which the rider sat, might be 1.5 metres tall or more, and the back wheel only a quarter as big. They look incredibly dangerous and unstable to us, and while looks can be deceiving, in this case they aren’t, especially considering the poor roads of the time.
The growing numbers of bicycle accidents led Englishman H. J. Lawson to invent the “safety bicycle,” which had a chain and sprocket driving the rear wheel, in 1879. Six years later fellow Englishman J. K. Stanley created a safety bicycle with wheels of equal size. After that, improvements came fast and furious: pneumatic tires in the 1880s, two and three-speed hub gears in the 1890s, and, just in time to kick off a brave new century of cycling, derailleur gears in 1899, the last major technological advance until the 1970s.
Bicycles are the most energy-efficient form of transportation, because they’re lightweight and barely make contact with the ground, which minimizes friction. (Energy efficiency isn’t necessarily a selling point, though, when the energy being used is yours — at least, that’s the way I feel some mornings facing the ride to work!)
A bicycle takes the pumping action of your legs, driven by the energy you derive from food and oxygen, and uses it to spin a wheel. Friction between the rear tire and the surface of the road drives the wheel forward, taking the bicycle — and you! — along.
Once you’re rolling, it becomes easier to balance on the bicycle. That’s because a spinning wheel has “angular momentum”: it likes to keep spinning at whatever angle it started spinning at, and resists being tipped. This resistance helps keep the bicycle upright. (Of course, tip it far enough, and gravity overwhelms angular momentum!) In effect, every bicycle has its own pair of stabilizing gyroscopes.
A bicycle also has the usual kind of momentum, the tendency of an object to keep moving in a straight line until acted upon by some other force. Unless you enjoy stopping by running into parked cars (an effective but drastic way to discover your own personal momentum, separate from that of the bike), you need brakes. Bicycle brakes are usually a set of rubber calipers that grip the hub of the wheel. The friction between the calipers and the hub drains energy out of the spinning wheel, turning it into heat.
The wheel is spun by a gear attached by a chain to another gear attached to the pedals. The ratio between the front and rear gears determines how quickly the rear wheel spins in response to one revolution of the pedals. If the chain is on a big gear in front and a small gear in back, you’ll find it hard to pedal but you’ll go really fast, because every time the front gear goes around, the little rear gear goes around more than once, taking the rear tire with it. It’s hard to pedal because it takes a lot of energy to spin the rear tire so quickly.
Vice versa, use a small gear in front and a large one in back, and you’ll find it very easy to pedal but very slow going, because now the rear wheel is spinning fewer times per pedal revolution — maybe not even once. This is useful for going up hills and against the wind, where you need extra energy to overcome gravity or air resistance.
The importance of these lower gears cannot be overstated, for there is one preeminent principle governing bicycles, known simply as the First Law of Bicycling:
No matter which direction you ride, it’s always uphill and against the wind.