The invention provides an insert for supporting a pneumatic tire which is intended to support substantially the entire internal face of the pneumatic tire and has a radially internal face intended to sit atop a wheel rim that accepts the pneumatic tire, has at least one cavity designed to be inflated by a valve of the wheel which valve is independent of the insert, via inflation gas conveying means opening onto said radially internal face and into said at least one cavity and discharge means for discharging the gas from this cavity, said at least one cavity and these conveying and discharge means being formed in and/or on the insert, the inflatable cavity being formed by an internal volume within the heart of the insert or alternatively by a concave external surface of the insert.