There is a growing body of empirical data supporting a gestural-based view of speech production in which adjacent speech gestures temporally and spatially overlap one another. Recent work suggests that certain acoustic measures are sensitive to changes in the overlap of adjacent consonant and vowel gestures [G. Weismer et al., J. Phon. 23, 111--126 (1995); E. Zsiga, J. Phon. 22, 121--140 (1994)]. Utilizing a graded speaking rate task, eight speakers produced 160 repetitions of ten target words embedded in a carrier phrase. F2 onset frequency, measured at the consonant--vowel boundary of test syllables, was used to index the degree of spectral-temporal overlap of adjacent consonant and vowel gestures. Regression analyses were used to evaluate the extent to which F2 onset predicted temporal variability in F2 formant trajectories due to speaking rate change. Results suggest that consonant and vowel gestures do not simply temporally slide away from each other with slowed speaking rate. Rather, modifications in the form and magnitude of vowel gestures are required to account for the present acoustic data. An empirically based acoustic model of variation in gesture overlap induced by speaking rate change is offered. Individual speaker differences also are discussed.