Applying material to a face I selected a single face in the object (car wheel, see picture) to be given a particular material (rubber, red color). However, when I press "assign" in the material tab, the whole object (wheel) is painted in the material. How can I limit this to the face?
The assign material button only works when there is more then one material.

When there is only one material the material is always on the entire model. To be able to use the assign button, just add another material.