No matter what kind of singing you do, classic, folk, or whatever, tone is sustained on the vowels. Consonants interrupt the tone and should be hit quickly and crisply (so people can understand the words). It's impossible to "sing" (i.e., sustain any kind of tone) on most consonants. T, D, P, B, K, Ch, maybe others. S comes out a hiss and is hardly euphonious, R is not much better. F, V, and Z, same deal. Try singing a G, J, L, Q, or W and see how far you get. How do you sing an X? Nasal consonants like M, N, and NG will sustain a tone, but might clear your sinuses at the same time.

With rare exceptions, when singing (or talking, for that matter) consonants are "touch and go." Unless you have some sort of speech impediment, it's hard to do it otherwise.

Don Firth