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Motorworld’s newspaper №85
Semi-track motorcycles began to be developed almost simultaneously with semi-track cars, since the late 1920’s. However, they weren’t widely spread.
The René-Gillet company played a big role in the history of French semi-track motorcycles. On July 31, 1931, André Maginot, French Minister of War, asked the René Gillet to test two off-road motorcycles. On April 10, 1933, Colonel Mammessier received a letter from René-Gillet with the results of tests: “As a response to your letter, we had the opportunity to present our prototype, on March 30, 1933, to General Bally and the staff of the Research Inspection Service & Technical Experiments of Artillery. General Bally asked us to make important changes to the first prototype and apply them in the design of the second prototype. We are engaged in this work, it should definitely improve the performance. We will deliver both prototypes as soon as we can.” The machine, built at the request of the Ministry of Defense, is worthy of the title of the monster Frankenstein: the monster with three caterpillar tracks, which replaced the wheels, weighed 600 kg. General Bally, aware of the non-viability of such a design, asked to change it, and on December 13, 1933, the René-Gillet presented the second prototype. It was a motorcycle with a J-type engine moved forward by 20 cm to shift the center of gravity.
The first test of the new machine, weighing 100 kg, was held on January 4, 1934. The machine was haunted by continuous failures: the caterpillar track was torn, the engine lacked traction and it constantly overheated, it was necessary to stop every 10 km and wait until it cooled. The average speed on a 6 km section was 25,714 km/h and the maximum speed was 36 km/h. It would take a long time to complete the design, but the company René-Gillet was busy with other military orders, so the tests were stopped on January 25, 1934.
In the second half of the 1930s, two more tracked motorcycles appeared. In April 1935, the “La Courtot” (“Palace”), designed by Henri Drescr, appeared. He used a 1000-cc engine of his own design. The tracks were made of rubber, turns were made by braking one of the tracks. The machine weighed 503 kg and consumed 12 times more fuel than the 750-cc Terrot . The motorcycle didn’t go into mass production.
The second tracked motorcycle was presented by Swiss inventor Adrien Mercier. The Mercier factory was located in France and produced 50cc mopeds with Lavalette engines, as well as 125/175-cc motorcycles with French Ydral engines. Since 1932, Mercier was engaged in the development of tracked motorcycles in a small French town Bois-Colombes, France. The military conducted the first test of Mercier’s invention on February 9, 1937, on hilly terrain with a steepness of ascent to 45% (27 degrees).
The Mercier tracked motorcycle was equipped with a 350cc OHV JAP engine, around which the whole design of the machine was concentrated. The rating of the JAP engine was 10 hp at 3,000 rpm which allowed moving at a comfortable speed up to 65 km/h. Additional cooling of the cylinder head was provided by a fan, which was driven by the engine.
The Mercier tracked motorcycles were launched with a kick starter, which could be reached even while sitting behind the wheel. Motorcycles were equipped with a three-speed gearbox with manual gear shifting, produced by the French company Soyer.
The front part was a complex construction with 150 mm wide rubber tracks and a suspension realized with semi-elliptic springs. The first prototype had a large armored shield, because of which the motorcycle couldn’t ride through the dirt. The rear part of the motorcycle turned out to be quite long and simple. To the tubular frame were attached: a saddle, footboards, a petrol tank, and a 270/90 rear wheel.
Despite the flaws of the prototype, the military found the prototype interesting and useful but didn’t order the motorcycle in industrial quantities.
Testing of the modified prototype No. 2 began on May 9, 1939, but the machine lost several rubber linings and the tests were resumed only on July 4th. The Mercier had to compete with the standard army motorcycle Sevitame. On the 147 km route, consisting of bad roads, Sevitame showed a higher average speed – 75 km/h against 66 km/h for Mercier. Mercier had a much higher cross-country ability, but the fuel consumption reached 17.6 litres per 100 km, compared to 10 litres per 100 km on the Sevitame. Another problem was overcoming 1.2 m mud trench. The Mercier track got bogged down, while the lightweight Sevatime overcame the ford. Despite these problems, the military recommended the production of a tracked motorcycle with a 540-cc Aubier Dunne engine but asked for some improvements.
Adrien Mercier refused to produce a third prototype because, in his words, “he spent a lot of energy and money”. On July 27, 1939, the project for possible mass production of the Mercier trike was closed.
|Years of manufacture||1937-1939|
|Quantity produced, units||less then 5|
|ENGINE AND TRANSMISSION|
|Type||Single cylinder, OHV|
|Engine capacity, cc||349|
|Bore and stroke, mm|
|Engine rating||10 hp at 3000 rpm|
|FRAME AND WHEELBASE|
|Frame type||Steel, tubular|
|Front suspension||Own design|
|Length, mm||2 250*|
|Height, mm||1 100*|
|Wheelbase, mm||1 385*|
|Ground clearance, mm||130*|
|Gas tank size, l||
|Maximum speed, km/h||