When we think of vehicles designed to push the boundaries of automotive engineering, the mind often drifts toward high-performance sports cars or powerful trucks. But there’s one vehicle that defies the traditional molds — the Michelin Test Citroen. In the early 1970s, Michelin designed a ten-wheeled Citroen known as the “Poids Lourd Rapide” or PLR, a heavy-duty test vehicle designed to test the durability of Michelin’s commercial truck tires at high speeds. This unique machine, often referred to as the “Citroen Centipede” or “Mille Pattes,” represents a fascinating chapter in tire technology and automotive history.

The Birth of the Citroen PLR: Purpose and Design

Back in the 1970s, Michelin needed an advanced solution to rigorously test its truck tires, especially given the ever-growing demand for commercial vehicle reliability. Traditional tire testing methods were insufficient to simulate the high-speed conditions under which commercial tires would typically operate. Michelin needed a custom-built machine to push tires to their limits — and that’s exactly what the Citroen PLR was designed to do.

The team at Michelin began by taking inspiration from the Citroen DS, an iconic French car known for its advanced design and engineering. The PLR was based on the Citroen DS platform, with a front-engine, front-wheel-drive configuration as the base. However, this was no ordinary Citroen. The team meticulously crafted a machine that would not only test the limits of Michelin’s commercial tires but also house the technology to push them to top speeds while ensuring data accuracy and safety.

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Check out the video “MICHELIN – Heavy-Duty Tire Test – The Mille Pattes” to see how Michelin tests their tires in action!

The Michelin PLR: A Technical Marvel

The Citroen PLR was a marvel of its time. With a bodywork inspired by the Citroen DS Safari, the machine was an imposing 21-foot-long behemoth. What set the PLR apart was its unique wheel configuration: 10 visible tires and a hidden 11th wheel used for testing. These wheels, sourced from the Citroen H van, served two key functions: the front four wheels were used for steering, while the remaining six were used for driving.

But it wasn’t just the wheel configuration that made the PLR unique. The hidden 11th wheel, located in the center of the vehicle, was used exclusively for testing large commercial tires. Suspended on a swing arm, this 11th wheel was hydraulically adjustable to different angles and speeds, allowing Michelin engineers to simulate tire wear and durability under real-world driving conditions.

Engine Power: Dual GM V8s for High-Speed Testing

To power such an enormous machine, Michelin turned to American muscle — specifically, two rear-mounted GM 5.7-liter small-block V8 engines. Each of these engines could produce 250 horsepower, giving the PLR a total output of 500 horsepower. This massive power was essential for the PLR’s intended purpose: to reach speeds that would test Michelin’s tires at the high velocities that they would experience in the field.

With its combined 500 horsepower, the Citroen PLR was capable of reaching speeds of up to 111 miles per hour, an impressive feat for a vehicle of its size and weight. To keep this powerhouse engine running cool, Michelin used five vertically stacked radiators, ensuring the PLR remained efficient even at its top speeds. Given its engine’s hunger for fuel, the PLR was equipped with dual 23-gallon fuel tanks, ready to fuel the beast through its grueling testing schedule.

Testing Tires at High Speeds: The Hidden 11th Wheel

What made the Citroen PLR truly groundbreaking was its tire testing methodology. The vehicle’s most innovative feature — the hidden 11th wheel — was used to test Michelin’s commercial truck tires at high speeds. As the PLR roared down the test track, the engineers had the ability to control the speed, load, and braking of the 11th wheel using a hydraulic system.

Michelin’s engineers used this hidden wheel to simulate extreme tire wear, testing how well the tires could handle the brutal conditions of long-distance trucking. Sensors strategically placed throughout the vehicle recorded the data, which was then analyzed in a laboratory to gauge how well the tires performed under different conditions. This system allowed Michelin to test tires for durability, load resistance, and other factors that are critical for real-world use.

Inside the Citroen PLR: Data Collection and Testing Conditions

Inside the Citroen PLR, the focus was entirely on tire testing. Michelin had designed the vehicle to ensure that all relevant tire data could be collected in real-time. The powerful hydraulic systems and sophisticated sensors enabled engineers to adjust the vehicle’s performance and measure tire performance across a range of conditions. These included factors like speed, load, braking capacity, and tire drift.

The Citroen PLR was more than just a test vehicle — it was a mobile laboratory that allowed engineers to gather important insights into how tires behaved at the very limits of performance. By simulating real-world conditions in a controlled environment, Michelin was able to refine its tire technology to meet the demands of the commercial trucking industry.

The PLR’s Legacy: The End of an Era and Its Final Resting Place

The Citroen PLR had a relatively short career, as advancements in testing technology soon led to more efficient methods. While its time in service may have been limited, its impact was lasting. The PLR demonstrated the incredible ingenuity of Michelin’s engineers and set the standard for future tire testing vehicles.

By the early 1980s, new technologies and automated systems had taken over, and the PLR was gradually retired from active service. Today, the vehicle resides in the Michelin Museum in Clermont-Ferrand, France, where it continues to inspire future generations of automotive and engineering enthusiasts.

Conclusion: The Citroen PLR’s Lasting Impact on Tire Development

The Citroen PLR represents a time when automotive engineers dared to build something entirely new — a machine capable of testing tires at the very edge of what was possible. While modern technology has advanced in ways that make the PLR’s testing methods obsolete, it still remains an important part of Michelin’s legacy in tire development. The PLR’s innovative design, powerful engines, and unique testing systems paved the way for future advancements in tire technology.

As we look to the future of tire testing and automotive engineering, we can’t help but be inspired by the creativity and ambition that went into the creation of the Citroen PLR. It stands as a testament to the visionaries who continue to push the boundaries of what’s possible in automotive technology.

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