Chataigner Report: comparative technical analysis of the Renault 4 CV (1948)

In this document

These two sheets are an excerpt from Mr. Chataigner's report dated 15 March 1948, copied onto a Citroën form ("SHEET NO. 1", no. 726 bis), dedicated to the technical analysis of the Renault 4 CV.

Dimensions and load distribution

The document provides the wheelbase (2100), the front/rear tracks when unladen, the rear engine (4 cyl. 55x80, 760 cm³), the 3-speed + reverse gearbox, and the Dunlop 5.0-15 tyres p. 3.

A table details the load distribution according to 5 configurations (unladen, 1 driver, 2 people in the front, 2 front + 1 rear, 4 people), with the rear load/front load ratio for each p. 3. The author notes that "the car is easier to drive with 2 people in the front" because the rear/front ratio is at its minimum there, and that this high ratio requires a higher rear inflation pressure than the front p. 3.

Suspension, steering and camber

The front suspension is described as a "transverse articulated quadrilateral - coil spring", the rear as a "suspended bridge - swing axle" p. 3. The steering is rack and pinion (reduction ratio 1/22.7, compared to the "Citroën PV: 1/13"), with 11° caster and a kingpin inclination of approximately 11°30' p. 3.

A table quantifies the camber variation during steering p. 3, followed on page 4 by the front and rear camber variation as a function of the load, as well as the variation in track and rear camber according to the suspension deflection p. 4.

Suspension flexibility

The report indicates a "practically linear" flexibility: 81 mm per 100 kg per wheel at the front (tyre only: 13.3%) and 53 mm per 100 kg at the rear (tyre only: 10%) p. 4. The author applies the rule f.front/f.rear = Load.rear/Load.front and concludes that the 81/53 = 1.53 ratio corresponds, according to the load table, to the "3 people" configuration p. 4.

The document ends on the disadvantage of an inclined roll axis, which "creates a general steering of the car" like a trailing or oscillating axle p. 4.

Context

The Renault 4 CV, launched in 1947, was at the time the main popular competitor to Citroën models. This type of comparative study — dismantling dimensions, load tests, camber measurements — was a common practice in automotive design offices to evaluate rival technical solutions, particularly regarding road holding and comfort.

In March 1948, Paul Magès joined the Citroën design office and was already working on suspension: his plans for hydropneumatic suspension with differential interaction date from 17 February 1944 (Plans for hydropneumatic suspension with differential interaction), and the first tests on the 2 CV would follow in May-July 1946 (Notebook of the first tests of the 2 CV with hydropneumatic suspension). This work would lead to the presentation of the DS on 6 October 1955.

Archivist's perspective

This document illustrates a competitive technical monitoring approach: it seems that Citroën systematically analysed rival suspensions to inform its own choices. The flexibility measurements and the inverse load/flexibility proportionality rule p. 4 directly evoke the concerns that would drive Magès' work on self-levelling.

This study can be compared to the Handwritten notes on self-levelling and front/rear flexibilities, which deal with a very similar problem, probably within the framework of the same internal reflections on the ideal suspension.