Bicycle

A bicycle is a two-wheeled machine that the rider balances by steering and drives with the legs, through pedals, a chain and a sprocket on the rear wheel. It grew from Karl Drais's wooden running machine of 1817 into the chain-driven safety bicycle of 1885, which, fitted with air-filled tyres, lets a person cover a given distance on a small fraction of the energy needed to walk it.

What it is

A bicycle carries one rider on two wheels set one behind the other. The rider sits on a saddle, keeps the machine upright by steering, and drives the rear wheel with the legs through pedals, cranks and a chain. It has no engine, and routine adjustments need only a few hand tools.

The plate shows a safety bicycle of the 1890s, the layout from which nearly every modern bicycle descends: two wheels of the same size, a frame of steel tubes forming two triangles, and tyres filled with air.

How it works

The rider balances by steering. When the bicycle begins to lean, the rider turns the front wheel slightly towards the lean, and the wheels run back underneath the rider’s weight. At walking pace the corrections have to be larger, which is why a slow bicycle wobbles.

The pedals turn two cranks fixed in opposite directions to an axle that runs through the bottom of the frame. A large toothed chainring on the right-hand crank pulls a roller chain, and the chain turns a small sprocket on the rear hub. With 44 teeth at the front and 18 at the back, one turn of the pedals turns the rear wheel about 2.4 times, and a wheel 70 cm across then rolls about 5.4 metres. Earlier machines with pedals on the front hub had no such gearing: the only way to travel further at each turn of the pedals was a bigger wheel.

The tyre of the 1890s: an inflated inner tube inside a cover of rubber and canvas.

A clean, oiled chain passes almost all the work of the legs to the wheel, up to about 99 per cent in laboratory tests. On level ground above about 30 km/h, three quarters or more of the rider’s effort goes into pushing air aside. For the same effort a rider travels about three times as fast as a walker, so a given distance costs much less energy; estimates range from about a third to a fifth of the energy needed to walk it.

A pneumatic tyre gives way around a stone instead of lifting the whole machine over it, so on rough roads it rides more smoothly and wastes less effort than the solid rubber tyres used before. Thin wire spokes, kept under tension, hold a light steel rim round and stiff.

How to build it

The running machine of 1817 had no pedals: the rider pushed against the ground with each foot in turn and slowed down with a cord-worked rear brake.

Drais’s machine was the work of a carpenter and a wheelwright: an ash beam, two wooden wheels with iron tyres, a front fork turning on an iron pin, a padded saddle, a board for the forearms and a rear brake pulled by a cord. The safest way to try the same kind of riding today is to turn a small, sound bicycle into a running machine, so that the frame, wheels and brakes remain those it was built with.

Choose the bicycle. It must be small enough for the rider to sit on the saddle, at its lowest, with both feet flat on the ground and the knees slightly bent, and it must have two hand-operated brakes, front and rear: a back-pedal (coaster) brake stops working once the chain is removed. Check that the frame has no cracks, that the wheels turn straight and that both brakes work.

Remove the drive. Take off both pedals with a pedal spanner; the left pedal has a reversed thread and unscrews clockwise. To remove the chain, open its joining link or push out a pin with a chain tool, or ask a bicycle shop to do it. If you have a crank puller, remove the cranks and chainring too, so that nothing can catch the legs.

Set the saddle. Lower the saddle until both feet rest flat on the ground, keeping the minimum-insertion mark on the seat post hidden inside the frame, and tighten the clamp firmly.

Test the brakes. Squeeze each lever while pushing the bicycle forward: the wheel must stop. If it does not, adjust the brake or have a bicycle shop do it before anyone rides.

Learn to glide. On a flat, quiet path, walk the machine astride, then push off with alternate feet and lift both for short glides, braking to stop.

Safety. Wear a helmet and ride away from traffic. Check the brakes, the wheel nuts or quick-release levers and the saddle clamp before each ride. Keep fingers away from turning spokes and from the teeth of the chainring if it is still fitted, and do not ride downhill until you can stop reliably.

History and evolution

Karl Drais, an official of the forestry service of Baden, rode his Laufmaschine out of Mannheim on 12 June 1817. Accounts of the trip give 13 to 15 km in about an hour; one timed run of 12.5 km averaged more than 12 km/h, over twice a walker’s pace. The machine was sold in France as the vélocipède from 1818 and copied in Britain as the hobby horse. A surviving example weighs 23 kg; surviving machines have a rear brake worked by a cord. Roads were poor, and interest faded within a few years.

On the high-wheel bicycle of the 1870s, the pedals turned the front wheel directly, so speed depended on the size of that wheel.

In the 1860s cranks and pedals were fixed to the front wheel in Paris. Whether the idea came from the carriage maker Pierre Lallement or from the workshop of Pierre Michaux is still argued. Lallement took it to the United States and received a patent on 20 November 1866; Michaux’s machines started the first cycling craze in France at the end of the decade. Their iron-shod wooden wheels earned them the English name of boneshakers. In the 1870s wire spokes and solid rubber tyres made wheels lighter, and the front wheel grew as large as the rider’s legs could reach. These high-wheelers were fast, but a rider who hit an obstacle could be thrown head first over the handlebar.

The safety bicycle solved this by putting the rider low between two small wheels and driving the rear one by chain. In 1885 John Kemp Starley built the Rover in Coventry; the machine kept in London weighs 16.8 kg and still has solid tyres. In 1887 or 1888 (sources differ) John Boyd Dunlop, a veterinary surgeon in Belfast, made air-filled tyres for his son’s tricycle, and patented them on 7 December 1888. The patent was later declared invalid, because Robert William Thomson had patented the same idea in the 1840s, but Dunlop’s tyres went into production in Belfast at the end of 1890. Within a few years the diamond frame and the pneumatic tyre were standard, and the safety bicycle was ridden by women as well as men. Freewheels, gears and better brakes came later without changing the layout.