The most efficient machine ever built.

The bicycle looks too simple to be a great invention, which is part of its genius. It has no engine, burns no fuel and has barely changed in over a century, yet on the pure measure of efficiency, how much distance you get from a unit of energy, a human on a bicycle beats every other animal and every other machine on Earth. It is the most efficient means of transport ever devised, and it runs on porridge.

It arrived in its recognisable form in the late nineteenth century, after a run of odd-looking ancestors including the enormous-wheeled penny-farthing. The breakthrough was the safety bicycle, two equal wheels, a chain drive to the back one, and soon pneumatic tyres, giving ordinary people a fast, cheap, self-powered way to travel that required no horse, no rails and no permission.

The social consequences were larger than the engineering. For the first time, working people could live further from where they worked, could reach the next town on a whim, could court someone from beyond the village. Its effect on women was especially profound. The bicycle demanded practical clothing, offered unchaperoned independence, and became so bound up with the fight for women's freedom that the American campaigner Susan B. Anthony said it had done more to emancipate women than anything else in the world.

And it never became obsolete. In an age of engines it simply kept being the right answer to a huge range of problems, and today, as cities choke on cars and heat, the humble bicycle keeps turning out to be the future as well as the past, quiet, clean, healthy and fair, a machine almost anyone can afford and repair.

The lesson is that elegance beats power more often than we admit. The bicycle solves the problem of moving a human being with almost nothing, no combustion, no complexity, no waste. The best design is frequently not the one with the most added, but the one with the least, doing the most.

Where are you reaching for an engine when the real answer is something lighter, simpler and almost free?