I don't know what breed, but I had a small-ish dog come out after me once while I was riding my lowracer. Speed was probably at more like 15 mph. I was basically eye-to-eye with it. There it was, snarling and snapping, almost at my elbow; so I extended my arm and clonked it over the head with my fist. His feet came out from under him and he went down chin-first into the pavement. My buddy was behind me and saw the whole thing; it's become one of his favorite stories.
I never saw that dog on the road again.