Phonological length is generally thought not to be relevant in Scottish English. However, some vowels are appreciably longer when followed by the past morpheme /d/ (instead of a tautomorphemic /d/), resulting in so-called `derived contrasts'. Do derived contrasts qualify as full-edged phonemic oppositions or should they be regarded as allophonic variation? In the current paper, which is a preliminary to perceptual experiments addressing this question, we quantify the differences in duration and spectral variation brought about by appending the dental suffix of the past morpheme to /u/, /i/, and /ai/. We show that consistent lengthening occurs for /u/ and /ai/, as well as stronger diphthongization in /ai/, which suggests that duration should perhaps be included in the vowel system of Scottish English.