|I'm not so sure about the 'less friction/more air' point. In my understanding, inline skates are capable of higher speed simply because of the larger diameter wheels that can be attached, but aggressive skates seem to be commonly made to take 55 mm wheels. Quads normally have 62mm. The idea of less friction can be disputed as well. Even though you have less contact area with a narrow inline wheel, the composition of most wheels made for a hard surface is softer, usually around 91A. Quad wheels for hard surfaces, or skateboard wheels mounted on quads, commonly have durometer ratings around 100A.