air cushion vs inner tube

air cushion

noun
  • A rubber or plastic inflatable cushion. 

  • A shock absorber that uses an air chamber. 

  • A layer of trapped air that supports a hovercraft. 

inner tube

noun
  • An inflatable rubber tube inserted into the casing of a pneumatic tyre/tire. 

  • Synonym of swim ring 

How often have the words air cushion and inner tube occurred in a corpus of books? (source: Google Ngram Viewer )