Self-supporting pneumatic tire

A pneumatic tire comprising a carcass comprising a reinforcing ply structure (12) extending between a pair of bead portions (14) and a pair of sidewalls (38), each sidewall (38) being located radially outward of one of the pair of bead portions (14); a tread (34); a belt reinforcing structure (28) located radially outward of the carcass and radially inward of the tread (34); and an insert (42) located in each sidewall (38) is disclosed. Each insert (42) comprises a plurality axially extending rib members (44) or is formed by a single piece having a varying axial thickness.