Handwritten notes on self-levelling: GMC/Pirelli-Paulstra comparison and flexibility calculations

In this document

Page 5: self-levelling and technical comparisons

The text, heavily crossed out, mentions difficulties related to self-levelling: it discusses "volumes to be displaced" and viscosity, with the author noting that it is "not surprising that delays in recovery cause swaying" p. 5.

A remark concerns the "shape of the piston on GMC": according to the document, this manufacturer claims to have designed its piston "to obtain, through section variation, a particular flexibility curve" p. 5. The author then judges that it "does not seem necessary to go further into the comparison of Citroën and GMC solutions", while acknowledging that "there is still quite a lot to say" p. 5.

The page breaks off on a sentence initiating a comparison with "the Pirelli-Paulstra solution" p. 5, without readable development.

At the bottom of the page, very faint pencil calculations appear: ratios and square roots, boxed figures (558, 345) and partially uncertain abbreviations ("NB", "Dyoclast", "NM", "Nord Ferrar") p. 5. Their precise meaning cannot be determined.

Page 6: flexibility and rigidity calculations (rear axle)

Under the heading "A.R." (Rear), a table of values contrasts two series of measurements:

Ratios are then calculated: "load 68/347 = 19.6" and "26.7/34 (0.78)"; "empty 26.7/228 = 11.7" and "68/22.8 = 3" p. 6. The results 19.6 and 11.7 are boxed, and 0.78 is circled.

Below these calculations, text in very faint ink is almost entirely illegible; only the acronym "CWC" can be distinguished, repeated twice, without usable context p. 6.

Context

These notes are, in all likelihood, part of the development work on the hydropneumatic suspension developed at Citroën, of which Paul Magès is the principal inventor. The comparison with competing solutions — GMC (General Motors) and Pirelli-Paulstra (French specialist in pneumatic suspension and elastic mounts) — corresponds to a common practice of engineers at the time, who benchmarked rival suspension systems (air springs, elastic blocks) before freezing their own technical choices.

The acronym "CWC" cannot be identified with certainty from the general knowledge available; it could refer to a supplier, a test, or a department, but this remains a hypothesis external to the document, unconfirmed.

Archivist's perspective

This document has the typical appearance of a working draft: crossings-out, deletions, pencil calculations superimposed on ink, figures boxed on the fly — likely notes taken "in the heat of the moment" by Magès while comparing the flexibility and rigidity performance of his suspension with those of competitors p. 5-6.

The main interest lies in the explicit comparative approach: Citroën vs GMC, then Citroën vs Pirelli-Paulstra, which sheds light on the development method through confrontation with market solutions rather than in a vacuum. The calculations on page 6, focused on the rear axle ("A.R."), seem aimed at quantifying the difference in behavior between a loaded and an unloaded vehicle — a central concern of the self-levelling suspension that Magès was developing.

The superposition of almost erased text under the calculations, with the barely perceptible "CWC" acronym, prevents any reliable further interpretation; this fragment could echo other technical notes in the same file, such as the technical note on the hydraulic transmission of high pressures or the excerpt from the Chataigner report on the Renault 4 CV, which also address suspension comparisons from the same period.