Magès's response to the Mines department regarding road-holding tests (7 Nov. 1970)

In this document

General response to letter AA.414.70

Paul Magès writes, for the BEA (Advanced Design Office), a handwritten response to the Mines engineer Mr. Gauvin, dated 7 November 1970 p. 12. He comments on a "draft instruction" relating to documentation and "road-holding" tests, dated 23 and 27 October 1970 p. 12.

Magès approves the principle of safety regulation, but questions a clause in the draft stipulating that these requirements would only apply to manufacturers who are "not notoriously known". He asks whether established manufacturers could thus continue to deliver vehicles "whose behaviour would merit improvement" p. 12.

On the technical documents to be provided

Magès deems the simple production of plans, perspective views or photographs insufficient to judge the behaviour of a vehicle p. 13. He notes that the draft asks for details on the front axle and steering, but nothing on the rear axle, which he considers "even more important" p. 13.

He also points out that the plans do not account for elastic deformations under load, as each manufacturer has its own empirical "little kitchen". At Citroën, he says, they strive to limit these deformations, "it costs us dearly" p. 13.

Finally, he notes that no precision is requested regarding the suspension, damping or front and rear roll stiffness, elements he deems "absolutely essential" p. 14. He proposes instead a one-fifth scale plan of the ground connection with dimensions, wheel loads and tyres p. 14.

On the proposed tests

Magès comments point by point on five envisaged tests p. 15-16:

Regarding test 5, he claims to know "cars that are half as rigid in torsion as others and that hold the road better", concluding that this factor is "negligible compared to the importance of the suspension", which is "not highlighted" in the proposed tests p. 15.

He adds that on a track with good grip and "in calm air", all cars behave well except for a few defects, and suggests testing instead on deformed or slippery surfaces, as well as in a straight line when crossing a road deformation on one side only p. 16.

Context

The Mines department is, in France, the body responsible for type-approving motor vehicles; its technical instructions then governed safety standards, including road-holding.

At Citroën, the hydropneumatic suspension, developed by Paul Magès and deployed notably on the DS then the SM, constituted a technical signature of the brand at that time — a system where dynamic behaviour depends heavily on the suspension rather than the pure rigidity of the body, contrary to the more classic approaches of the competition.

Archivist's perspective

This document illustrates Magès's role as a technical expert consulted by his hierarchy (the BEA) when facing an external administration, in an argumentative and pedagogical register rather than a purely technical one.

He defends, page after page, a thesis consistent with the whole of his work: the suspension is, according to him, underestimated in the assessment of road-holding in favour of more visible criteria such as body rigidity p. 15. This plea echoes another note from the same day, the Magès note of 7 November 1970 on road-holding regulations (response to engineer Gauvin), which seems to deal with the same exchange with the Mines.

The tone mixes defence of Citroën expertise — not without a touch of pride regarding the cost of designs "influenced as little as possible by deformations" p. 13 — and commercial concern regarding a possible obligation to align with less demanding competing practices.