Since the velar region of the roof of the mouth is relatively extensive and the movements of the dorsum are not very precise, velars easily undergo assimilation, shifting their articulation back or to the front depending on the quality of adjacent vowels. They often become automatically fronted, that is partly or completely palatal before a following front vowel, and retracted, that is partly or completely uvular before back vowels.
Palatalised velars (like English /k/ in keen or cube) are sometimes referred to as palatovelars. Many languages also have labialized velars, such as [kʷ], in which the articulation is accompanied by rounding of the lips. There are also labial–velar consonants, which are doubly articulated at the velum and at the lips, such as [k͡p]. This distinction disappears with the approximant consonant [w] since labialization involves adding of a labial approximant articulation to a sound, and this ambiguous situation is often called labiovelar.
A velar trill or tap is not possible according to the International Phonetics Association: see the shaded boxes on the table of pulmonic consonants. In the velar position, the tongue has an extremely restricted ability to carry out the type of motion associated with trills or taps, and the body of the tongue has no freedom to move quickly enough to produce a velar trill or flap.