From Longman Dictionary of Contemporary Englishinner tubeˈinner tube noun [countable] 
TTCa rubber tube filled with air that is inside a tyre
TTCa rubber tube filled with air that is inside a tyreExamples from the Corpus
inner tube• Cut a 5/8in wide band of bicycle inner tube.• The mix is pumped gently down the inner tube, out through the bottom and up the outer tube.• The inner tube is negatively charged and the outer tube is made positive. 