Draft commercial notice: comfort and road holding of the 15 H

In this document

Comfort: the initial observation

The text opens by recalling that, apart from the solution adopted on the 2CV Citroën, no truly significant improvement had been made to automotive suspensions for several years p. 121. The author explains the classic compromise: the more the flexibility of the springs is increased, the more the action of the shock absorbers must be reduced, but a theoretically ideal damping would make the car unpleasantly "stiff" p. 121. Weaker shock absorbers provide a suppleness considered by some to be incompatible with road holding — an idea that the document disputes from the outset p. 121.

The technical solution

To break out of this compromise, it was necessary to "increase flexibility in considerable proportions (5 to 6 times on average)" p. 122. Steel being ruled out due to weight, the text describes a compressed gas enclosed in a steel sphere, whose elastic force is transmitted by a liquid to a piston connected to the suspension arm, with gas and liquid being separated by a deformable membrane p. 122. An automatic system regulates the quantity of liquid to maintain the car at a constant height regardless of the load p. 122. Damping is achieved by laminating the liquid in valves placed between the sphere and the suspension cylinder p. 122.

Application to the 15 CV and sales pitch

At the front of the 15 CV, the weight not justifying a pneumatic suspension, it was limited to maximum flexibility and an anti-roll bar; the comfort is consequently superior at the rear p. 123. This is followed by scenarios intended for salespeople: reading, writing, filling a glass and drinking from it, or sleeping while comparing with another car on the same journey p. 123. The automatic height adjustment ensures correct headlight adjustment, and the author suggests trying "the automatic rear wheel lifting device even in the event of a puncture" p. 123.

Road holding

The dedicated section asserts that "it is the 15 Citroën that has the best road holding" p. 124 and details the progress of the rear axle: independent wheels, increased rigidity of the wheel-body connection, shock absorbers "with instantaneous action without any dead travel", and great flexibility combined with sufficient damping for aperiodicity p. 124. At the front, the flexibility has been "more than doubled" with an anti-roll bar p. 124. The document insists on the reduction of variations in contact force with the ground, deemed "unbeatable" on very bad roads p. 125, and warns salespeople that they must advise the client that the comfort is so different that one must learn to "feel" their new car p. 125. The text concludes by acknowledging that the 15 "leans a little more in corners" without this altering the road holding p. 126.

Context

The document mentions the 2CV and the 15 CV Citroën, iconic models of the brand in the 1950s. The 15 CV (six-cylinder Traction Avant) precedes the DS, presented on 6 October 1955, whose hydropneumatic suspension would generalize the principles described here — compressed gas, sphere, membrane, height corrector — to all four wheels. This connection with the DS is a matter of general historical knowledge and is not mentioned in the document itself.

This 1954 text is situated in the career of Paul Magès at the Citroën design office, where he worked from 1939-1940 and where he recorded the first plans for hydropneumatic suspension on 17 February 1944 (Hydropneumatic suspension plans with differential interaction (17 February 1944)), followed by the first tests on the 2 CV in 1946 (Notebook of the first 2 CV hydropneumatic suspension tests (May-July 1946)) and the test of the 15-Six H on 3-5 April 1954 (Road test of the 15 Six H (ELV 412) by Paul Magès, 3-5 April 1954), which is the same year as this draft commercial notice.

Archivist's perspective

This text appears to be a commercial pitch aid written to train salespeople, rather than an internal technical note: the pedagogical tone, the concrete scenarios (reading, writing, sleeping) and the demonstration recommendations attest to this (p. 123, p. 125). It allows us to understand how Paul Magès and his teams translated the technical advances of the compressed gas suspension into sales arguments accessible to the general public.

This document is in the same vein of studies as the plans for hydropneumatic suspension with differential interaction, ten years earlier, which laid the technical foundations popularized here for the clientele.