In this study we explore how acoustic and lip articulatory characteristics of bilabial consonants and three extreme French vowels vary in Lombard speech. In the light of several theories of segments perception we have shown that formant modifications should decrease the audio intelligibility of vowels in noise. On the contrary, modification in lip articulation should improve the visual intelligibility of vowels and bilabial consonants. This is not in agreement with previous studies which reported a global increased intelligibility of Lombard speech especially in the audio domain and not a lot in the visual one. Thus, more detailed research is needed about the segmental and prosodic contribution to the increased intelligibility of Lombard speech.