The pneumatic tire

A pneumatic tyre carries its load on air. Inside a tough outer casing of rubber reinforced with fabric plies sits an inflatable tube; pumped hard, the trapped air becomes a spring stiff enough to bear the vehicle yet soft enough to deform around every stone and rut. The casing takes the wear and grips the road; the air does the cushioning. The key is that the spring is the gas, not the material — which is why a tyre a few millimetres thick can soak up shocks that would shatter a solid wheel, and why it rolls easily: instead of grinding over each bump, the contact patch flexes and lets the wheel float across.

Every wheel before it was rigid — iron-shod wood, then solid rubber. On a road of stones and ruts a rigid wheel transmits every jolt straight to the frame and the rider, and it fights the road, wasting energy climbing each small obstacle instead of rolling over it. Cyclists called solid-tyred machines "bone-shakers" and meant it. The pneumatic tyre cut both the shaking and the rolling resistance at once, and that mattered far beyond comfort: within a few years, when the automobile arrived, it was the only thing that let a heavy vehicle travel fast on a real road without hammering itself to pieces. No air cushion, no practical high-speed road transport.

Dunlop was a veterinary surgeon in Belfast. In 1887 his young son found his tricycle hard going on solid tyres over the cobbles, and Dunlop wrapped the wheels in thin rubber sheet formed into tubes, inflated them, and bound them on with canvas. It worked so well he patented it in 1888 and it went quickly into bicycle racing and manufacture. But the idea was not new. Robert William Thomson had patented an air-filled tyre — rubberized-canvas tubes inside a stitched leather cover — in 1845, and demonstrated it running smoothly and quietly for over a thousand miles; rubber was then far too costly for it to sell, and it was forgotten. When Thomson's old patent resurfaced, Dunlop's was declared invalid in 1891. His name lived on as a tyre company, though he himself sold out early and profited little.

The pneumatic tyre powered the bicycle boom of the 1890s and then became indispensable to everything that followed it onto the road: the motorcar, the truck, the motorcycle, and the aircraft undercarriage that must survive the shock of landing. It is one of the few nineteenth-century inventions still built to its original principle — air held under a fabric-reinforced rubber casing — on very nearly every wheeled vehicle that moves people and goods over ground today.