Detailed note from Magès to engineer Gauvin on road-holding regulations

In this document

This handwritten note, dated 7 November 1970, is Paul Magès's response to a letter from the Mines engineer Mr. Gauvin (referenced "AA.414.70", dated 29 October 1970) concerning a draft regulation for road-holding tests.

A question on the fairness of the regulation

Magès immediately questions a clause providing that the documents and tests required "will never be requested from notoriously well-known manufacturers" p. 17. He sees a risk of inequity: "small manufacturers" would be checked while large ones could continue to deliver vehicles "whose behavior would deserve improvement" p. 17.

The limitations of the requested documents

He judges that drawings, perspectives, or photographs do not allow for judging the actual behavior of a vehicle p. 18. He notes an inconsistency: the list of required documents details the front axle but not the rear axle, "yet this is even more important" p. 18. He also points out that static diagrams do not account for elastic deformations under load p. 18-19.

Citroën practice and the forgotten suspension

Magès mentions the "little tricks" specific to each manufacturer p. 19 and asserts that at Citroën, they seek to obtain diagrams little influenced by deformations, which "is expensive" p. 19 — while worrying that this internal requirement might end up harming commercial competitiveness against the competition p. 19. He notes above all the absence, in the list of requested documents, of any mention of the suspension, damping, and roll stiffness, "a primordial influence" according to him p. 19.

On body rigidity and proposed tests

Regarding the test for torsional and bending rigidity of the body, he claims to know "cars that are half as rigid in torsion as others and that hold the road better" p. 20, and judges this criterion negligible compared to the suspension. He reviews tests 1 to 4 (maximum speed, behavior under lateral acceleration, lane changing, zigzag), questioning the test conditions (surface condition, coefficient of adhesion) each time p. 20-21.

In conclusion, he proposes that a one-fifth scale drawing of the vehicle's road-holding system, with wheel loads, tire dimensions, and steering ratio, serve as a sufficient reference document p. 21, and requests a meeting with engineer Gauvin p. 22.

Context

The Mines department, in France, oversees vehicle type approval. In the early 1970s, the issue of road-holding became a growing regulatory challenge, in a context where Citroën hydropneumatic suspensions (inherited from the DS, then applied to the SM) stood out clearly from the classic metallic spring solutions used by the competition.

Archivist's perspective

This document, more developed than another response from Magès to Gauvin dated the same day, seems to be a reworked version where the engineer refines his technical argument point by point.

It illustrates Magès's unique position: defending Citroën's artisanal and costly expertise in road-holding, while resisting a regulation he deems technically poorly calibrated — notably its silence on the suspension, which was nevertheless at the heart of his own work as an inventor. The numerous erasures and revisions p. 17-21 testify to a text in the process of being drafted, probably intended to be cleaned up before being sent.