Barthélemy note to Allera and Magès on the reversed DX front axle (14 December 1966)

In this document

This two-page technical note, signed by Barthélemy and addressed to Allera and Magès, responds to a request for analysis concerning a "reversed DX front axle" — that is, the DS ("DX") front axle mounted backwards to allow for the installation of another powertrain p. 87-88.

Mechanical and structural constraints

Barthélemy lists fourteen problems. He first points to the path of forces from the wheel to the body, then to the increased loads on the axle arm bearings: when cornering (10° steering angle, 0.8 g), the overload on the lower arm would reach +50%, a figure attributed to "Mr. Hondet" p. 87. He also notes an increase in the camber of the outer wheel (± 40') and a reduction in ground clearance of approximately 30 mm at the arm support p. 87.

Next, the cross-members connecting the half-axles are discussed (rigidity, weight, space requirements related to the gearbox profile), as well as the question of overall weight, compared to the "DX front unit" already reinforced several times in 1955, 1962, and 1965 p. 87.

Steering, cooling, safety

Page 88 addresses a steering/wheel interference beyond a 40° steering angle, requiring either a limitation of the steering angle or a redesign of the tie rod p. 88. Also listed are: the modification of the arm support related to the caster (1°40', DX series), engine cooling with electric fans, the clearance between the anti-roll bar and the gearbox, as well as reservations regarding repairability and safety in the event of a front impact, the rigid subframe being considered unfavourable in a collision p. 88.

Barthélemy's conclusion is clear: he does not see how to solve all these problems and advises against adopting this solution p. 88.

A handwritten annotation in red, added later, specifies: "There was nothing inaccurate in what is written. But the 6-cyl. engine [...] could not be mounted on the car without reversing the axle. The SM was built and a general compromise was found" p. 88.

Context

Although not named in the document, the later annotation explicitly refers to the Citroën SM, presented in 1970 with a Maserati V6 engine. Historically, the integration of this larger engine in front of the front axle did indeed require rethinking the architecture inherited from the DS, whose front axle remains designated here by its internal code name "DX".

Archivist's perspective

This document illustrates the preparatory, technical, and cautious work that precedes a major industrial decision. Barthélemy, in response to a request from Allera and Magès, draws up an uncompromising assessment of the difficulties of a reversed axle solution — an analysis which, it seems, informed the trade-offs leading to the SM.

The red handwritten addition, written after the fact (probably by Magès or a close collaborator), is valuable: it confirms the accuracy of the initial analysis while revealing that a "general compromise" finally allowed the vehicle to be built p. 88.

This document is in line with the reflections on the DS suspension and chassis conducted by Magès, as evidenced by the note on the AP suspension of 22 February 1963.