An air tube (12) of elastomer material for tyres is described, which is divided into at least two parts by an internal wall (19) extending in the equatorial plane and delimiting a central core (20) and two sidewalls (21) in said air tube. The core is formed of the above wall from the ends of which two flanges (22, 23) issued perpendicularly to the wall itself issue perpendicularly to the partition itself, in opposite directions, over a predetermined length; the flange and sidewall ends are associated with each other by vulcanization and the core rigidity is greater than the sidewall rigidity. The air tube performs the function of supporting the tyre not only during normal running but also under deflated conditions, as in the case of a puncture in one of the two air tube parts, for example. In particular, the air tube is advantageously used with 'low-section' tyres (1) as it has such features that it expands within the available space between the tyre and related mounting rim.