Gnome et Rhône

A Parisian workshop, 1905

Louis Seguin was not a motorcyclist. He and his brother Laurent were engine men, and in June 1905 they set up the Société Des Moteurs Gnome in Paris to build engines for cars. It's a useful place to start the Gnome et Rhône story precisely because the company's motorcycles, which is what most people searching this page actually want to know about, were never the point. They were a sideline, born of circumstance two decades later, grafted onto a business whose real ambitions lived in the sky.

The Seguins' engines found their calling in aviation. Gnome's rotary designs, in which the whole cylinder block spun around a fixed crankshaft, gave early aircraft a power-to-weight ratio nothing else could match, and by the years before the Great War the firm was one of the most important aero-engine builders in France. A rival outfit, Société des Moteurs Le Rhône, was building its own well-regarded rotaries at the same time. The two companies entered into negotiations during 1914, and the formal merger that created Gnome et Rhône was completed on 12 January 1915 — a single firm now controlling much of French rotary engine production at the exact moment the war made that production existential.

Engines for a war, then a peace with no orders

What Gnome et Rhône did during the First World War was extraordinary by volume alone. Between 1914 and 1918 the company built some 25,000 examples of its 9-cylinder Delta and Le Rhône 110hp rotary designs, with a further 75,000 produced under license by other manufacturers across the Allied nations. For four years, a huge slice of the aircraft engines powering the war in the air, on both sides of various fronts through licensing arrangements, carried Gnome et Rhône's design DNA.

Then the war ended, the military contracts evaporated, and Gnome et Rhône — like the aircraft maker Blériot and plenty of other firms suddenly stripped of wartime orders — had factories, skilled labor, and no obvious product. Motorcycles were the answer, at least for a while. Gnome et Rhône took the pragmatic route of building the British ABC under license rather than starting from a blank sheet.

The ABC arrived in France through André Barthélémy, its Parisian distributor and, more usefully, a capable engineer in his own right. The original British ABC design was clever but fragile, and Barthélémy is credited with sorting out a number of its mechanical weaknesses — enlarging the engine's capacity to 500cc, reworking the carburetion and rocker gear, and fitting an oil cooler to a design that ran hot. Gnome et Rhône kept developing the ABC after that, releasing a refined 493cc version in 1921 that stayed in production until 1925.

Finding its own voice: the 1920s

By the early 1920s Gnome et Rhône was ready to build motorcycles of its own design rather than someone else's under license. The first of these was the Model B, a 500cc side-valve single with a three-speed gearbox. There is conflicting information about its exact timeline — some accounts place its debut at the 1920 Paris Salon, others put full production starting the following year — but either way it marked the moment Gnome et Rhône stopped being an ABC licensee and started being a motorcycle manufacturer in its own right.

The company's ambitions grew through the decade. The Model D, a side-valve 499cc Grand Sport unveiled at the 1923 Paris Salon, was a genuinely accomplished machine for its day: 10 horsepower at 2,800rpm, chain drive front and back, a three-speed gearbox, drum brakes, and a top speed around 100km/h. It spawned a family of D2, D3, and D4 variants and became the backbone of Gnome et Rhône's competition effort through the rest of the decade.

Ownership shifted in 1922, when Paul-Louis Weiller, a decorated World War I flying ace, took control of the company. Weiller's instinct was to pull Gnome et Rhône's center of gravity back toward aircraft engines, which remained the firm's larger and more strategically important business even as the motorcycle line continued alongside it.

Gnome et Rhône had actually abandoned horizontally opposed engine layouts in its motorcycles around 1924, but the flat-twin idea did not stay buried. In 1930 the company returned to it with the V2, a 500cc flat-twin with shaft final drive carried in a stamped-steel frame — a construction method that would become something of a signature. The V2 evolved into the CV2, with overhead-valve gear, launched in 1932.

The Model X era and the road to war

The mid-1930s produced what many collectors now regard as Gnome et Rhône's finest motorcycles. The Model X, debuted in 1935, took the flat-twin formula further: a 724cc OHV engine, a four-speed gearbox, shaft drive, and the pressed-steel chassis construction the company favored. Paired with a Bernardet sidecar tub on its own purpose-built chassis, the Model X combination was a serious, well-engineered touring and sidecar platform, and fewer than 500 examples of the related XA model were built before the range moved on.

What came next was aimed squarely at military and police buyers. The AX2, introduced in 1937, carried a larger 800cc side-valve flat-twin and, distinctively, drove its sidecar wheel as well as the rear wheel of the motorcycle itself — a genuinely useful feature for rough terrain and one that marked the AX2 out from ordinary road-going sidecar rigs. It stayed in production through the Second World War, with Gnome et Rhône supplying engines and machinery to the occupying German forces during that period, an uncomfortable but well-documented fact of the company's wartime existence.

Racing and record runs

Gnome et Rhône motorcycles built a genuine competition reputation between the wars, much of it tied to two riders whose names appear again and again in period accounts: Henri Naas and Gustave Bernard. The Model D series was the vehicle for a string of victories through the 1920s and into the 1930s, and the pairing of Bernard and Naas — sometimes described as an inseparable double act — kept collecting wins on Gnome et Rhône machinery for years, with Bernard's competition career extending even beyond the marque's own golden period.

The high point came in 1937, when Georges Monneret took 24 world records at the Montlhéry banked circuit outside Paris, including a 12-hour run at an average speed of 146km/h — genuinely rapid for a road-based motorcycle of the era. The Model X, in dual-carburetor tune producing around 38 horsepower, was credited with more than 100 competition victories and records over its life, including an endurance run of over 50,000 kilometers.

Postwar, the marque's small two-strokes reportedly kept up the tradition of long-distance stunts. Period French motorcycling press is said to have reported a run by three students on Gnome et Rhône R3s from Paris to New Delhi, and separately Gustave Bernard is sometimes credited with a fast Paris-to-Madrid dash. Neither claim has been independently corroborated beyond the original period reporting, so they're worth treating as marque folklore rather than settled record — the kind of story that gets repeated at owners' club meetings whether or not anyone can produce the paperwork.

Nationalization and the long wind-down

The war left Gnome et Rhône, like much of French heavy industry, in a position the state was not willing to leave to private ownership. The company was nationalized on 29 May 1945 and folded into what would become Snecma, France's state aircraft engine combine. The Gnome et Rhône name did not disappear overnight, though — motorcycles and even bicycles continued to be built under the Gnome et Rhône badge for some years afterward. In the postwar reorganization the company also found itself linked with Société des Aéroplanes Voisin, and for a period both names appeared on the same machines.

The postwar motorcycle line moved decisively toward small, practical two-strokes rather than the prewar flat-twins. The Type R series — the R and R1 at 100cc, the piston-ported R4 at 125cc producing around 6 horsepower — were simple, unit-construction machines built for a France that needed cheap transport more than it needed sporting flat-twins. A 500cc model was reportedly on the drawing board when Gnome et Rhône finally wound down motorcycle production toward the end of the 1950s, closing out roughly forty years of building bikes alongside its far larger aviation business.

What remains

As a motorcycle manufacturer, Gnome et Rhône is gone — has been for well over half a century. But the parent lineage never stopped: the aviation side of the business carried on inside Snecma, building engines for military and civilian aircraft, and today lives on as Safran Aircraft Engines, one of the larger names in the global jet engine business. It's an odd afterlife for a marque best remembered by enthusiasts for pressed-steel flat-twins and sidecar rigs.

Among collectors, that's exactly where the interest sits. Gnome et Rhône motorcycles — the flat-twin Model X and CV2 in particular, and the military AX2 sidecar combinations — are valued as well-engineered artifacts of a specific, brief period when a major aero-engine manufacturer decided motorcycles were worth doing properly rather than as an afterthought. Original, unrestored examples are scarce; the company's move into two-strokes after the war never carried quite the same weight with collectors as the prewar flat-twins did. For a marque that spent most of its existence building engines for airplanes, Gnome et Rhône left behind a surprisingly durable reputation on two wheels.