This paper proposes that closed syllable laxing and open syllable tensing of non-low vowels are motivated by conflicting strategies of contrast enhancement in vowel–consonant sequences. Laxing enhances the distinctiveness of consonant contrasts by allowing for more distinct VC formant transitions, in particular in sequences involving a non-low vowel followed by an oral labial/coronal/velar consonant (e.g. [p t k]). Tensing enhances the distinctiveness of vowel contrasts by providing more distinct formant realisations for vowels. Linguistic variation results from different ways of resolving the tension between maximising vowel dispersion and maximising consonant dispersion. Laxing typically applies before coda consonants as a way to compensate for the absence of good perceptual cues to place of articulation. The hypothesis that laxing enhances the distinctiveness of postvocalic place contrasts is supported by a study of mid-vowel laxing in French, which corroborates the general claim that perceptual contrast plays a role in shaping phonotactic restrictions.