The Wheel

The wheel is one of the world’s most important inventions. It is the key to motion and plays a huge part in society today. Present everywhere on all our cars, trains, ships, planes, machines, and wagons; wheels play an integral role in industrial technologies and consumer products. Their rolling motion is the basis of many mechanisms such as pulleys, gears, cams, and bearings. Wheels are one of the oldest technologies, with roots around since the beginnings of recorded history.

Throughout time, wheels have evolved. Around about 3500 BCE, wheels were wooden disks, developed from the use of logs as rollers. Spokes were introduced in 2000 BCE, as they considerably reduced the wheel’s weight assisting better motion. They also gave it a resilience that ‘cushioned’ travel over rough terrain.

19^th century wagon wheel production has been of great interest to me recently. Wheelwrights created functional works of art from raw materials like wood and iron, having only experience to rely on; no books or education. Formal procedures of modern engineering such as materials selection, stress analysis and fracture mechanics, were carried out intuitively. The hub, spokes and felloes (sections of the rim) were shaped using the simplest of hand tools. Each spoke was hammered into a felloe and hub, without the use of bolts, screws or glue.

Many aspects of the wheel were thought through to make it suitable for purpose. Firstly, each of the wheel’s components required wood with specific properties. For example, ash, beech, or elm would be preferred for the rim, because of their flexibility and toughness, so the rim would be easy to shape as well as able to withstand the harsh conditions it would be put through. Secondly, large diameter wheels reduced the force required to pull the wagon. Thirdly, the wheels were dished, with the top of the dish facing outward from the wagon. This has shown to increase the wheel’s strength toward lateral forces, so the wagon could resist the effect of any side-to-side motion. If the wheel were perfectly flat, this motion would tend to bend and finally break the spokes. The outward slant also allowed the wagon body to be tapered outward, increasing its load-carrying capacity.

I have been reading ‘Masterworks of Technology’ by E. E. Lewis and would recommend it to everyone with an interest in engineering.