Halliday & Matthiessen (1999: 197):
The expanded form of the nominal group makes explicit the systematic taxonomic relationship which links one thing with another: it is clear that (theoretically at least) a touring bike is a kind of bike, a bicycle wheel is a kind of wheel. It is always possible, of course, to expand in a metaphorical way, as with cart wheel (in turning cart wheels) and Catherine wheel (a kind of firework); these are not, strictly speaking, kinds of wheel, so we have to recognise either that these fall outside the taxonomic organisation or that the taxonomy itself is being extended metaphorically. But this does not affect the general principle at work; indeed, it is the taxonomic principle which makes such divergence possible.