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Which wore the 10-wheel big-engine tire-testing configuration better? Citroen or Cadillac?

Published in blog.hemmings.com

Period photos likely via Michelin, Biel Technicum.

Technical solutions often appear that only make sense in certain windows of time. Take, for instance, the fax machine, relevant until suddenly everybody had email. Tire testing apparently also had a need for ever more complex solutions in the 1970s, which is why, in a short window of time, two different 10-wheel mobile tire testing machines were built in Europe, one from a Citroen DS, the other from a Cadillac Eldorado.

The former is perhaps the better known of the two. Michelin, builder of truck tires as well as passenger car tires, wanted to test their largest offerings at speed without risking expensive vehicular damage as a result of a blowout. So in 1972, the company – which at the time owned Citroën – built its Poids Lourde Rapide, a.k.a. the Mille Pattes (millipede), using a number of Citroën parts. The DS panels are obvious, the hydropneumatic suspension less so, and the 10 wheels all used hubs from the automaker’s H-series van.

Four of those 10 wheels steered the rig. While dual steering axles are rather uncommon here in the States, European truck manufacturers employ them on a more regular basis. The other six drove the car, taking power from a Chevrolet 350-cu.in. V-8. Then Michelin added a second 350 to power the big hydraulically lifted truck wheel and tire – the whole raison d’etre for the vehicle – mounted in the center of the PLR. Plenty of heavy shielding kept tire explosions from wrecking the PLR’s innards.

Michelin could reportedly get the PLR up to 111 MPH while testing it on the Ladoux test track – not bad for a rig that weighed 21,000 pounds. The tire company has held on to it since retiring it from service and currently displays the PLR at L’Aventure Michelin.

Despite their similarities, the Cadillac is considerably less well known than the PLR. Up until 2016, the only mention of it on the Internet seemed to be an all-too-brief entry on it in Yann Saunders’s Cadillac database, tentatively attributing its construction to Sbarro (the coachbuilder, not the pizza chain) based on its location in Switzerland and Sbarro’s penchant for building oddly configured cars. Indeed, Sbarro did build an Eldorado-based six-wheeler “executive car” in 1978 called the Function Car.

But then more of the story came to light thanks to French website SixMania, whose writers followed along as an anonymous friend of theirs bought the 10-wheeled Eldorado. As SixMania reported, German car dealership Willscheidt in Nordrhein-Westfalen, which continues to specialize in American cars today – built the Eldorado in 1975 for Ingenieurschule Biel in Switzerland.

The school reportedly needed “a rolling laboratory for measuring tire friction under different load conditions,” and the Eldorado platform appeared ideal due to its size, front-wheel drive, and big ol’ Cadillac engine. In fact, Willscheidt added two more fuel-injected 500-cu.in. Cadillac V-8s in that giant caboose appended to the Eldorado. Of note, while the PLR’s test engineers apparently had to sit cramped in the back with the big tire bomb, the Eldorado’s test engineers got a second cockpit just above and behind the Eldorado’s stock passenger cabin.

Somehow, with more engines and a greater overall length (378 inches versus the PLR’s 283 inches), the Eldorado came in at just 8 tons or so and topped out at 99 MPH. According to Saunders, the Eldorado remained in service until 1998. At some point, the Eldorado wound up back in Lohmar and was put into storage before its current owner bought it and exported it to France.

We still have so many questions. Did the Willscheidt people benchmark the PLR when building the Eldorado? Was the latter’s sunset-stripe color scheme consciously chosen or just a happenstance of the moustache-laden late Seventies? What were the Eldorado’s other two engines doing? Were the Eldorado’s test engineers dangling their feet on the Eldorado driver’s ears? If both the PLR and the Willscheidt Eldorado exist, will we ever see a head-to-head drag race? And, if so, can we then follow that up by pitting the Willscheidt Eldorado against the Australian eight-wheeled Eldorado?

(H/T to Samuel Addison of the society of eccentric automobile in art, culture, politics, and design.)