This paper deals with ASR for two languages: Hausa and Wolof. Their common characteristic is to appear with vowel length contrast. In other words, two versions (short / long) of a same vowel exist in the phoneme inventory of the language. We expect that taking into account this contrast in ASR models might help and this is what we investigate in this pilot study. The experimental results show that while both approaches (vowel length contrast modeling or not) lead to similar results, their combination allows to slightly improve ASR performance. As a by-product of ASR system design, we also show that the acoustic models obtained allow a large scale analysis of vowel length contrast for phonetic studies.