Quantity-sensitive stress languages typically stress the heaviest syllable in a word. Segments in the syllabic nucleus (i.e. the vowels) and in the coda (i.e. the post-vocalic consonants) contribute to syllable weight; pre-vocalic consonants (syllable onset) add no weight. This study presents a phonetic explanation for the weightlessness of the syllable onset. Both a speech production and a perception experiment were carried out On the assumption that syllable weight can be operationalised in terms of duration, the production data provide no support for the weightlessness of the onset added onset consonants contributed as much, if not more, to syllable duration than consonants added in the coda. However, the perceptual data provide a clear correlate of the weight difference between onset versus nucleus and coda. The results of a duration adjustment task indicate that variations in the onset consonant are not heard; identical variations in the coda consonant are reproduced adequately, whilst variations in the vowel are even perceptually overestimated.