K.I.T.T has the ability to fold himself into a more aerodynamic shape. He folds the trunk into the backseat, thus eliminating it, making himself smaller. He widens a little for added stability on the road, and lowers himself to the ground a few inches. This form allows him to achieve speeds of 450mph and more , but doing so is dangerous.
Each of KITT's bodies has a different way of folding itself. For example, as the Dodge Ram he folds in the truck bed, tightening the distance between his wheels. He has used this feature rather creatively in the past.
Never, ever, do that again. Ever. - Pierce
I made it up the elevator in one piece. - K.I.T.T