A radial ply runflat tire (50) having a tread (52), a carcass (60) with two sidewalls (77,78), one or more radial plies (70,72), two annular beads (36a′,36b′), and a belt structure (56) located radially between the tread and the radial ply structure (58). The tread has laterally disposed tread ribs (64a,64b) whose contours are defined by circular curves intersecting nontangentially with the circular curve that defines the contour of the central portion of the tread. Each sidewall portion (77,78) has a rib (63a,63b) that is out of contact with the road during normal inflation operation and that engages the road during runflat operation. The tread ribs (64a,64b) are separated from the respective sidewall ribs (63a,63b) by decoupling grooves (65a,65b) which overlie the point of nontangential intersection of the circular curves that define the respective contours of the sidewall ribs and the laterally disposed tread ribs. Decoupling grooves (66a,66b) overlie the point of nontangential intersection of the circular curves that define the respective contours of the laterally disposed tread ribs (64a,64b) and the central portion (54) of the tread.