Can you still remember the TRX tire that was mounted on BMW and various French cars in the late 1970s and 1980s? It was an attempt by Michelin to reinvent the wheel, at least the tire. The TRX was introduced in 1975 and was only available in a metric (millimeter) size instead of the usual inch size.
There was, however, another line of thought behind it, as the TRX was a revolutionary design for high speeds that needed a special rim and could not be mounted on existing, conventional rims. To prevent this from happening, this tire was only available in a metric size. At the time a great idea, but nowadays extremely awkward if you are looking for new rubber goods for your now classic Citroën CX or something ...