Comparative test of TPV suspension, 10 May 1948: A6, A 11 bis and PV

In this document

Test protocol

The test was carried out on 10 May 1948 at La Ferté, 'road along the property wall', in the presence of Messrs. Cadiou, Magès and Renault p. 65. It aims to compare 'fluidity and small shocks with 2 people and 50 Kgs' between a standard A6 and an 'interaction' car named A 11 bis p. 65. Both vehicles are equipped with 125 1/2 HSP tyres, similar cold pressures (front 1.100 / rear 1.200 on the workshop gauge), a 375 cc engine, and the same front seat, that of the A 11 bis p. 65.

Initial conclusions

Cadiou, front passenger, notes that the A 11 bis is 'as fluid as the A6', or even superior regarding vertical body accelerations p. 65. However, it transmits 'a series of small continuous shocks of the nature of wheel beats', forming a 'continuous background rolling' felt in the floor, the bodywork and the seats, whereas the A6 only presents 'very slight vibrations in the floor' p. 65.

Effect of tyre pressure

After driving, the pressures had risen to 1.300 (front) / 1.400 (rear). They were then lowered to 1.000 (front) / 1.100 (rear), i.e., 850/950 on the standard gauge p. 65. Under these conditions, the A 11 bis retains a 'small continuous jolt in the seat' but loses its major floor vibrations; the A6, for its part, 'has almost no more vibrations in the floor and can be considered very good' p. 65.

Comparison with the standard PV

The same test conducted with a standard PV, at identical speed, shows 'very few vibrations in the floor', comparable to those of the deflated A6, but 'the harshness of the suspension is transmitted entirely by the seat' p. 66. The report concludes that a softer seat could dampen this effect on this type of road p. 66.

Context

The acronym TPV refers, in Citroën history, to the 'Toute Petite Voiture' (Very Small Car) project which would lead to the 2 CV — a context external to the document, not mentioned as such in the transcribed pages. Research into 'interaction suspension' conducted at that time by Paul Magès extends the hydropneumatic suspension plans with differential interaction and automatic levelling dated 17 February 1944, and heralds the work that would lead, after the first tests of the 2 CV with hydropneumatic suspension in 1946, to the hydropneumatic suspension of the DS presented in 1955. The comparison with a PV (Citroën front-wheel drive) and an A6 (Renault) places this test in a post-war automotive benchmarking context.

Archivist's perspective

This document illustrates, very concretely, the empirical test method practised by the Magès team: direct road comparisons, pressure variations, sensory feedback from the passenger. It shows that in 1948 the 'interaction' solution was not yet perfected — it corrects certain defects but introduces others (vibrations transmitted to the seats) — which explains the continuation of research leading, a few years later, to the tests of the 2 CV and then to the hydropneumatics of the DS.

The mention of a softer seat as a path for improvement p. 66 is interesting: it suggests that at this stage, the envisaged solution relied as much on the contact element (seat) as on the suspension itself. This document can be compared with the Hydropneumatic suspension plans with differential interaction and automatic levelling, which date back four years and set the theoretical foundations for the system tested here in real conditions.