Numbers sum up the Michelin PLR pretty well. Weighing about 20,200 pounds, it has two rear-mounted engines, 16 cylinders, 10 wheels, and a top speed of about 100 mph. It kind of looks like a Citroën DS, but it’s a lot wilder under the sheet metal than the familiar headlights suggest — and that’s where the story gets even more interesting than the jaw-dropping numbers. The PLR is a one-of-a-kind prototype built by Michelin to test tires for semi trucks and buses, which were traveling faster and faster in the early 1970s.
Officially, Michelin named its DS-like rolling laboratory the Poids Lourd Rapide (PLR), which translates to “fast semi truck.” Unofficially, the wagon was called Mille-Pattes, which means “centipede” in French. The fun little nickname alluded to the test mule’s configuration. While it’s shaped like a bloated DS, it was a one-off with four steerable wheels in the front, six rear wheels, and a tire-testing lab behind the seats.
Michelin retained the height-adjustable hydropneumatic suspension system, some of the interior bits and pieces came from the DS parts bin, and the wheels and the hubs were borrowed from the Citroën H van. Keep in mind that Michelin owned Citroën at the time, so using as many off-the-shelf parts as possible made sense to keep production costs in check. With that said, there’s not much else that carries a Citroën parts number. Power comes from two (yes, two!) Chevrolet-sourced 350-cubic-inch V-8 engines, each rated at 200 horsepower. One engine drove the car, while the second powered the aforementioned on-board test lab.
All told, the PLR measured approximately 283 inches long and 96 inches wide. It was difficult to miss, but Michelin painted it in orange and yellow to ensure that it truly couldn’t be missed when it was out testing.
The PLR first turned a wheel (pun not intended… or was it?) in 1972 on a test track located in Ladoux, a small town that’s about 20 minutes north of Michelin’s headquarters in Clermont-Ferrand, France. Its main purpose was to help engineers test the company’s truck and bus tires at high speeds, under high loads, or both, without crashing. Testing new tire technology in real-world conditions, such as by driving a semi at 95 mph around a track to find out whether or not the rubber stayed in one piece, could have resulted in serious situations.
In a nutshell, the tire that needed to be tested was mounted onto a wheel and bolted to a hub in the trunk. An intrepid engineer would then drive the PLR onto the track, build up speed, and lower the hub until the tire made contact with the ground. An on-board hydraulic system allowed the driver to apply up to 7700 pounds of pressure to the tire or change the camber angle. Speed and braking tests were carried out as well. The data recorded by sensors during each test was later printed out to be analyzed in a lab.
The PLR retired in the early 1980s, and Michelin hasn’t built anything like it since. Luckily, scrapping such a unique vehicle wasn’t an option. It joined the manufacturer’s collection of historically relevant vehicles, documents, objects, and, of course, tires, and it’s now one of the most fascinating displays you can check out while visiting the Michelin museum. It apparently still runs, and it’s occasionally taken out for events.
