Focus on machines: Bi Som Trac


The Bi Som Trac is hardly as well known as Essex’s Doe Triple-D in the UK, but this French-built machine represents the pinnacle of tandem tractor development and remains a fearsome beast in the field.

Tandem tractors date back to the days when not only was engine power limited, but also the components needed to get that power to the ground. Pairing two together, to be driven by one person, made a lot of sense.

More than the sum of their parts

Earnest Doe and Sons of Essex are considered pioneers in this field, but it was also tried by others like Bolinder in Sweden and by a Someca dealer in France who ran the project in a very similar way to Earnest Doe .

Bolinder experimented with the tandem concept. The prototype was built by a local engineering company on his behalf

In the 1950s and 1960s the demand for power and grip was as great in northern France as it was in the UK, and by doubling two 45hp tractors a 90hp machine could be produced with a traction provided by four large wheels.

The logic was impeccable, and it is suggested that such conversions were not as rare as one might now think.

It’s also worth noting that many of these conversions have been designed to be uncoupled when not needed, leaving two tractors free for lighter duties.

There are accounts of local engineers and enthusiastic farmers creating their own variations on the theme from different brands of tractors, though few, if any, originals exist today.

Doe triple D tandem tractor
The Doe Direct Drive, or Triple D as it was more commonly known, was first created by a customer

This was indeed the case with the design of the Doe Triple D which was based on a conversion by one of the company’s customers who connected two Fordson Power Majors together and then asked Doe’s to build a better version, giving birth of the legend.

The Doe Triple D was intended to be kept as a single unit, but many were separated later in life to release two smaller tractors, with a higher selling value than the original machine.

Someca tractors

The French company involved was Ets Lhermitte, then a Someca dealer just west of Paris; it now has six branches and owns the John Deere agency for the region.

Like many continental businesses, the Someca name is an acronym rather than taken from the founder; in this case it is the Société de MECAnique de la Seine.

Someca 30B from 1961. Tandem France
Someca 30B from 1961. Around 40 would have been imported to Ireland. This very well preserved example belongs to Alan Mitchel, Co. Offaly

It was created in 1951 to assemble tractors built under license from Fiat (another acronym) as an offshoot of Simca (another acronym), which had itself been created to manufacture Fiat cars in France in the 1920s.

In 1957, he experienced his first real success with the launch of the Someca 40 which proved to be a very popular tractor throughout France.

Never enough power

As excellent as these machines were, Ets Lhermitte’s customers needed more power to cover the largest fields on the French plains more efficiently.

Tractor Someca 40 Saint Loup
The Someca 40 establishes the brand in France

An earlier trip to the UK by company staff had introduced them to the Triple-D and so it was after that the Bisom 40, two Someca 40s in tandem, was created to meet demand.

Although we can’t be absolutely sure today, it seems that while the Triple D was created to provide the traction needed to plow Essex’s heavy clays more efficiently, the Bisom 40’s purpose was to deliver power supplement for all crops.

Bisom 40 Someca France
The Bisom 40 was based on two Someca 40 units and was designed to quickly return to individual tractors on the farm

In both cases, the existence of larger tools to cope with the power available became a problem and their use was therefore limited to some extent.

This would certainly explain the ease of uncoupling the French machine which, with practice, would not take more than an hour and a half.

Bi Som Trac Fiat Someca two-seater
Implements large enough to cope with the extra power provided by Tandem tractors had to be purpose-built

There was also the issue of the PTO – although it had more than twice the traction, due to all the weight being carried by the drive wheels, shaft power was limited to what was available at from the rear unit.

Disappearing from the scene

Although the first Bisom 40 first appeared around 1969, it was not clear when production would end, although, being a secondary line to the main business of selling Someca tractors, there perhaps had no well-defined production line or schedule.

The Someca 40 was discontinued in 1964 and it is believed that some time later Tandem models were built based on the 55 hp Someca 511, but again, with tractors changing from single units to tandem and vice versa -versa, it would be difficult to pin down the exact story.

Ford County Wheels Drive Someca
In the late 1960s, other manufacturers joined the equal four-wheel-drive club, including County and, a little later, Massey Ferguson.

However, throughout the 1960s, standard tractors were becoming more powerful, eroding the benefits that these tandem units offered.

Production of the Doe Triple-D finally ended in the late 1960s with two Ford 5000 units providing 150 hp. Over 300 had been built in total.

Born again with the Bi Som Trac

This could have been seen as the end of the idea, but it was briefly revisited in France in the 1980s where a few Fiat-based machines were created and sold as Bi Som Tracs.

These were dedicated tandem machines that were not designed to be split. They relied on six-cylinder Fiat units of 100 hp each with the pivot point immediately in front of the cabin.

Tandem tractor Someca bi som trac long nose
The long nose designed to achieve a 50-50 weight distribution proved to be the main flaw of the tractor

The traction and performance were said to be exceptional, but the long nose was its downfall, even on the large flat terrain of its home territory.

It required a lot of room to turn, and the front engine housing was vulnerable to uneven ground, especially when crossing catwalks.

Damaged engines and oil spills were not uncommon and only a few were built, two of which still exist today.

The example shown here belongs to Jean Pierre Noret who showed it at the Retro Moisson event, held every August in Saint-Loup, central France.

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