Variations on the vehicle include:
I'd like to see a discussion of the social implications of the bicycle. It helped to strengthen the gene pool for rural workers. It tripled their courting radius on the one day per week they had off and thus helped reduce rural inbreeding. The two wheeled, diamond frame safety bicycle (basically the same one we ride today) gave women unprecedented mobility, freed them from corsets, and contibuted mightily to women's emancipation. In cities, it helped reduce crowded inner city tenaments, but allowing workers to commute from single family dwellings in suburbs. It helped reduce dependence on horses. It allowed people to travel in the country. It was three times as efficient as walking and three to four times as fast.
What we really need is a picture:
And an article on bicycle repair and maintenance.
The picture should label the following parts: frame, top tube, down tube, seat tube, seat post, headset (head set?), handlebars, front forks, rear forks, chain stay, rear stay, wheel, wheel rim, wheel axle, spoke, spoke flange, brakes, brake levers, saddle, bottom bracket, crankshaft, cranks, pedal, chain, chainring, rear gears. Also the parts which vary a bit more: toe clips, cleats, gear changers, hub gears, derailleur gears, front gear block, rear gear block (aka cassette), mud guards, chain guards (both on the stay and around the chain), lights, panniers.
An article on bicycle brake systems might be useful.
And maybe at least one reference to a sports science article that explains how cycling is the most efficient form of human powered transport.
It has often been observed that a fish is not likely to need a bicycle.
Another form of two wheeled vehicle is the push cycle.