Barometers Realm

This miniature Pocket Tire Pressure Gauge, dating to around 1930 and produced by the renowned company Michelin & Cie (Clermont-Ferrand, France), was manufactured in the first half of the 20th century as part of the brand’s motoring accessory set. The presence of a dual scale made the instrument convenient both for the European market (metric system) and for countries where pounds per square inch were traditionally used (such as the United Kingdom and the United States).

The gauge has a round case with an elongated nozzle, made of nickel-plated brass, which gives it a silvery sheen and protects the surface against corrosion. The back is smooth and slightly convex, without decorative elements. The connecting nozzle is cylindrical with a small central opening for admitting air from the tire. On the lower part of the case is a small brass lever used to reset the pointer to zero after a measurement. The dial is made of painted aluminum with a matte light surface, with inscriptions applied in black and red paint. At the center is the marking “MICHELIN & Cie / FLORA / Clermont-Ferrand.” The scale features two concentric ranges: the upper black scale indicates pressure in kilograms per square centimeter (kgf/cm²) from 0 to 3, while the lower red scale reads pounds per square inch (psi) from 0 to 40. The pointer is made of blued steel, painted black, and has a slender form with a sharp tip.

Inside the instrument is a Bourdon tube, bent in an arc and placed around the perimeter of the case. Its free end is connected via a small linkage to a toothed sector, which in turn drives a pinion mounted on the pointer’s axis. This mechanism allows the pointer to rotate along the scale. All parts are made of brass and steel, assembled into a simple movement that operates through the elasticity of metals and light friction, without the use of complex bearings.

The principle of operation is based on the elastic deformation of the Bourdon tube. When the gauge is connected to a tire, air enters the tube, and under pressure it tends to straighten. Its free end moves the linkage, which through the transmission system rotates the pointer on the dial. Pressure is displayed simultaneously in two systems: metric (kgf/cm²) and imperial (psi). After measurement, the pointer can be returned to its starting position by pressing the reset lever.

Following the First World War (1920s), pocket tire gauges became widespread in Europe as automobiles increasingly adopted Michelin pneumatic tires. By the 1930s, such instruments had become a signature motoring accessory. The Second World War (1939–45) interrupted large-scale production, and postwar instruments were often simplified and standardized.

In the well-known journal La Vie Automobile (Sixième année. 1906. N°223, January 6, 1906 – N°274, December 30, 1906) one can read the following lines:

"Another novelty with which Michelin has gifted us this year is a device given the name pressure controller… The essence of the new instrument is that the Michelin controller is screwed onto the place of the valve cap. Once a closed circuit is formed, a special plunger releases the valve, and air flows freely into the manometer. Everything occurs smoothly and gently. The tightness of the connection is ensured by leather washers, while the return of the plunger is provided by a small spiral spring. There is no doubt that the Michelin controller will soon be found not only in shops but also in every toolbox."