It’s summertime in Saskatchewan, and that means the roads are full of joggers, walkers–and bicyclists.
The first 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, like Fred Flintstone.
A German baron, Karl von Drais, added a steerable front wheel in 1817, creating the “draisienne,” or dandy horse. In 1839, Kirkpatrick Macmillan, a Scottish blacksmith, added pedals which drove the rear wheel by means of cranks.
In the 1860s the French invented 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 meant that the larger the front wheel, the faster the bicycle. This led to the “pennyfarthing” bicycle, on which the front wheel 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 they were.
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 derailleur gears in 1899, the last major technological advance until the 1970s.
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 bicycle forward.
Road bikes and touring bikes generally have thinner tires than mountain bikes. The thin road tires are inflated to 100 or even 120 PSI, so they don’t flatten out much. That means less surface area contacts the road, which means less friction and more speed.
Wide mountain bike tires flatten out more on a hard asphalt surface, making it harder to pedal the bike, but on a dirt trail, the fatter, softer tires float on top of the rough surface. A thin, hard road tire would cut deep into the dirt.
Once you’re rolling on any kind of surface, it becomes easier to balance on the bicycle. Scientists aren’t sure why. One theory, which makes intuitive sense, is that it’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.
Recently, British scientist David Jones set out to create an unrideable bicycle. He built a bike in which the gyroscopic action of the front wheel was cancelled out by a wheel mounted next to it that rotated in the opposite direction–and found that it didn’t affect either the stability or steerability of the bicycle. Which may mean the spinning wheels don’t have anything to do with stability at all, and scientists will have to look elsewhere for an explanation.
Like any other moving object, a bicycle tends to keep moving in a straight line until acted upon by some other force. 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 bicycle’s rear wheel is spun by a gear attached by a chain to another gear attached to 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. 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.
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.
