For many years since the 80's I have driven many Citroen DS and after that Citroen CX's as daily drivers
Originally the Citroen DS sphere was basically 2 screwed together parts
View attachment 1846565
DS Sphere
and de CX spheres were totally sealed and closed
View attachment 1846566
CX Sphere
Both spheres were interchangeable, only they were pressurized on a different nitrogen pressure.
When the CX sphere came out (interchangeable) a lot of DS drivers complaint about them because they didn't have the same comfort level, the Citroen Gurus at that time explained that because the membrane of the CX sphere was a little smaller then the original Citroen DS sphere it gave a little harder ride and therefore also Citroen had tried to balance it this by giving it a higher pressure of nitrogen.
After some time these complaints faded away slowly as people couldn't compare them anymore as the citroen DS Spheres had become NA.
I'm not sure but it seems to me that the diameter of the Pleiades spheres looks a little smaller then the OEM Sphere
Do the Pleiades and the OEM have the same diameter on the widest point ?