hardtop vs wheels

hardtop

noun
  • The removable rigid roof of a convertible or sports car. 

  • An indoor cinema with a roof, as opposed to a drive-in. 

  • A car with such a roof. 

wheels

noun
  • An automobile or other vehicle; a set of wheels. 

  • Well-developed thigh muscles. 

How often have the words hardtop and wheels occurred in a corpus of books? (source: Google Ngram Viewer )