Letter from A. Bougeard to Paul Magès regarding 2 CV suspension tests (5 November 1959)

In this document

This letter is addressed by A. Bougeard, who operates a cider mill and distillery in Vitré (Ille-et-Vilaine), to Paul Magès at the Citroën "Studies" department, dated 5 November 1959 p. 2. It bears the reception stamp "- 6 NOV. 1959" and an annotation "Received on 12/11. 8am (Mr. Cadion)" p. 2.

Load tests on the experimental 2 CV

Bougeard reports on tests conducted by varying the number of occupants. At full load (4 people "of large build"), "a minimum of 7 kg is necessary" and the car is then "really good" p. 2 — this passage is underlined in red in the original. With a lighter load (3 people, only 1 in the back), the front remains satisfactory but the rear is judged "a bit hard". With only 2 people in the front, a pressure of "5 1/2 - 6" is sufficient at the front, the rear being "even harder" (underlined in red, p. 2).

He draws a technical conclusion from this: reducing the rear lever arm would require a pressure of 8 to 10 kg under load, which would harden the front; shortening the front lever as well would only shift the same problem p. 2.

Proposed modification

On the advice of a mechanic, Bougeard identifies that the external capacities only contain "3 holes of 5 m/m" as air passages between cylinders and capacities, which "restricts the passage of air" and makes larger piping useless p. 3. He plans to widen these holes, even if it means "calibrating them later with jets", and to add, at the rear only, "one-litre capacities to each cylinder on the compensation side" p. 3.

He announces his intention to finish these modifications "by the end of the week" and proposes a test with Magès on "Thursday the 12th" (corrected to "Thursday the 19th" by a handwritten annotation) or Friday the 14th p. 3. Finally, he mentions the exchange of a grey 2 CV for a blue 2 CV made available to him by Mr. Delérive p. 3.

Context

This correspondence is part of the research conducted at Citroën in the late 1950s on compensated pneumatic suspension systems, in parallel with the development of the hydropneumatic suspension applied to the DS. Exchanges with external testers, who had test vehicles in real-world use, were among the common methods of development before the era of systematic test benches.

Archivist's perspective

This document concretely illustrates the empirical method of adjusting an experimental suspension: it is through daily use and trial and error (pressures, hole diameters, capacity volumes) that Bougeard refines his device, before any theoretical feedback from Magès.

It seems that this 2 CV is part of the same test programme as the handwritten note of 24 June 1959 on the effects of one capacity per side or per axle, the question of capacity sizing being directly related here to field experience. The subject will likely find a continuation in the minutes of the meeting of 17 February 1960 on the Bougeard patent, which seems to close or formalise this collaboration.