hardtop vs roadster

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. 

roadster

noun
  • An open automobile having a front seat and a rumble seat. 

  • A person who lives along the road. 

  • a sea-going vessel riding at anchor in a road or bay. 

  • A clumsy vessel that works its way from one anchorage to another by means of the tides. 

  • A bicycle, or tricycle, adapted for common roads, rather than for the racing track, usually of classic style and steel-framed construction. 

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