Time/speed conversion tables and hourly speeds in 3rd gear

In this document

Page 27: time / speed conversion table

This typewritten sheet presents a six-column table alternating "Timed time" / "Speed in kilometres" p. 27. It allows for the conversion of a time measured with a stopwatch — presumably over a reference distance — into a speed expressed in km/h. The values range from a time of 6'00" corresponding to 10 km/h, up to 34" corresponding to 106 km/h p. 27. The table is drawn with a ruler in purple ink and bears a stamp p. 27.

Page 28: hourly speeds in 3rd gear

This second sheet, titled « VITESSE HORAIRE (3ème vitesse) » [HOURLY SPEED (3rd gear)], typewritten in purple ink, cross-references several parameters: torque, wheel dimensions and engine speed expressed in revolutions per minute (rpm), from 1000 to 4000 rpm with a mention of « affolem » (probably "affolement" [valve bounce]) at the end of the series p. 28.

Two sets of wheel dimensions appear (140x40, 150x40, 160x40), combined with two torque/gear values ("8 x 31" and "9 x 31"), with associated powers ranging from 13 CV to 42 CV depending on the rpm p. 28. The calculated speeds are given with high decimal precision:

A small illegible handwritten mark appears at the top right of the page p. 28.

Context

This type of conversion table and hourly speed calculation belongs to the classic automotive engineering methods of the interwar period and the 1940s-1950s, a period during which engineers often had to establish, without calculators or spreadsheets, charts cross-referencing engine speed, gearbox ratio, tyre dimensions and actual vehicle speed.

At Citroën, these hourly speed calculations by gearbox ratio were commonly used during road tests or on test benches to verify the theoretical performance of a vehicle or engine. However, nothing in the document allows these tables to be linked to a specific Citroën model.

Archivist's perspective

These two sheets seem to constitute practical work tools, probably intended to facilitate the analysis of speed tests (page 27) and the theoretical calculation of performance in 3rd gear (page 28), rather than a test report as such.

The absence of any date or mention of a vehicle makes it impossible to place them precisely in the chronology or in a specific test file of Paul Magès. Their manufacture — typewriting in purple ink, artisanal layout using punctuation — however, evokes a working method similar to other technical documents in the collection, such as the Hotchkiss-Laffly 6-wheel vehicle test report, which could belong to a similar period and engineering practice.

These are likely reference charts, kept and reused over several test campaigns, which would explain their generic and undated nature.