Recent research has revealed substantial between-speaker variation in speech rhythm, which in effect refers to the coordination of consonants and vowels over time. In the current proof-of-concept study, the hypothesis was investigated that these idiosyncrasies arise, in part, from differences in the tongue’s movement amplitude. Speech rhythm was parameterized by means of the percentage over which speech is vocalic (%V) in the German pronoun “sie” [zi+]. The findings support the hypothesis: all else being equal, idiosyncratic %V values behaved proportionally to a speaker’s tongue movement area. This research underlines the importance of studying language-external factors, such as a speaker’s individual tongue movement behavior, to investigate variation in temporal coordination.