Michelin’s 10-wheeler ‘frankenstein’ Citroen test vehicle

Ever since the first car was invented, engineers have made them faster and faster, resulting in greater demands on many areas of the vehicle. Not only did the stresses on the drivetrain and bodywork increase but the tyres – which kept the car ‘stuck’ to the road – also faced new demands.

Michelin, a leading tyremaker, understood the importance of ensuring that tyre technology kept pace with the increase in car performance as safety was crucial. The same applied to trucks as well, with greater loads on tyres as payloads rose with more powerful engines available. The stresses on tyres are enormous and they kept increasing over the years.

Creating a ‘frankenstein’ vehicle
Although computers were already used in the 1970s, relying on simulations is not enough and actual testing with prototypes must also be done – under extreme conditions. This led Michelin to develop a unique test vehicle that some saw as a ‘frankenstein’ the way it was designed.

Because Michelin was a shareholder of Citroen at the time, the test vehicle was based on a Citroen DS with a DS Safari stationwagon grafted on. When it was first shown to the public in 1972, it was referred to as Poids Lourd Rapide, which means ‘fast truck’, but with its multiple tyres, it was quickly nicknamed ‘Mille Pattes’ (centipede).

10 wheels + 1 more inside
The monstrous 9,150 kg vehicle – 7.27 metres long, 2.45 metres wide – had 10 wheels, with 6 at the rear end and 4 at the front. There were 3 rear axles from a Peugeot 504 and right at the back were two Chevrolet V8 Chevrolet engines, each with a capacity of 5.7 litres and able to produce 250 bhp. The automatic transmission had 3 gear ratios and Michelin engineers built their own gearbox.

Actually, there were 11 wheels but the eleventh one was not visible as it was inside the vehicle. One engine drove the vehicle and the second engine provided additional drive for the wheel in the middle which would carry the tyre being tested. This was usually a large truck tyre and it was held on a swing arm which could be hydraulically lowered and adjusted to different angles during the test drive. A hydraulic cylinder was used to apply loads of up to 3,500 kgs.

This allowed the engineers to adjust not only the speed and braking, but also the load and drift of the central wheel to test the tyre in every sort of condition. Sensors recorded data as the vehicle went up to speeds as high as 180 km/h, and the data was later analysed in the laboratory.

The bodywork was necessarily large mainly to enclose the test tyre; in the event of its bursting or breaking up, it would be safer and the 10 wheels also provided better stability in such a dangerous situation. Each of the 10 wheels had a 16-inch diameter and 205/55 R size.

New testing equipment replaces Centipede
By the early 1980s, other methods of extreme testing of truck tyres were developed to do the Centipede’s job. Computers were also getting more powerful so more complex simulations could be run. Nevertheless, real-world testing is still part of the tyre development process.

As for the ‘Centipede’, it was not scrapped and is today displayed at the Michelin Museum in France.

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