Dunlop put air inside a tyre so it cushioned itself

In the 1880s bicycles and tricycles ran on solid rubber tyres. On the cobbled streets of Belfast those tyres made every passing whoops a jolt, and John Boyd Dunlop, a veterinary surgeon, watched his nine-year-old son struggle with exactly that on his tricycle.

Dunlop knew rubber and he knew surgery. In October 1887, in the yard of his Belfast home, he fitted an inflated tube of sheet rubber around a wooden disc 96 centimetres across, then rolled that wheel and a plain metal wheel across the yard together. The metal wheel stopped almost immediately; the pneumatic one kept going until it hit a gatepost and rebounded. He put pneumatics on both rear wheels of the tricycle, and the improvement was immediate and obvious.

The clever part is not the tube but the air inside it. A solid rubber tyre is nearly incompressible, so the bump it cannot absorb is passed straight into the frame and the rider. Air is compressible, so when the tyre hits a stone the air deforms, spreads the load, and then returns to shape because the tube is sealed. The rubber is only the container; the air is the spring.

Dunlop patented the invention and it was granted on 7 December 1888. Unknown to him, a Scot named Robert William Thomson had patented a pneumatic tyre in 1846 and 1847, so Dunlop's patent was later declared invalid — but Thomson's had never been commercialised, and it was Dunlop's practical, usable version that the bicycle and motor industries adopted.

Air-filled rubber tube carries load

Solid rubber is nearly incompressible, so it passes the bump straight through instead of absorbing it.

Air is compressible, so it deforms on impact and spreads the load over a larger tyre footprint.

A sealed tube keeps the air at pressure, so the tyre springs back instead of flattening.

Dunlop had the rubber skills and the practical test case, so his version worked when the earlier patent never went anywhere.

When a material fails by being too rigid, do not make the material softer — make the support a medium that is genuinely compressible, like air, and seal it so it springs back.

A cyclist using Dunlop's tyres began winning, drawing the attention of Harvey du Cros, who formed a company with him to exploit the invention. Dunlop sold his rights for a small sum and a small shareholding and withdrew in 1896. His patent was later ruled invalid because a Scot, Robert William Thomson, had patented a pneumatic tyre in 1846 and 1847, but the company bearing his name went on as Dunlop Rubber. Dunlop made no great fortune, yet the air-filled tyre became the basis of the modern motor vehicle.