Safety pneumatic tire for passenger cars

A safety pneumatic radial tire for passenger cars comprising a pair of bead cores, a pair of sidewall portions, a tread portion extending across the two sidewall portions in a ratio R/S of 1.2/1 to 2.5/1, where R is the curvature of the inner surface of the tread portion and S is the maximum width of the tire exclusive of any protection rib, at least one carcass ply containing cords embedded therein and extending across the two bead cores in a substantially radial direction, a belt reinforcing layer arranged between the carcass ply and the tread portion, a viscous rubber puncture-sealing layer arranged on the inner circumferential surface of the tread portion, an annular protection rib on at least one side of the sidewall portions and coaxial therewith, said protection rib having a substantially trapezoidal cross-sectional shape, the vertical height of the middle position of the outer end and inner end of the protection rib from the bead base portion being positioned less than at the maximum width position of the tire therefrom but being at least 35% of the height of the cross-section of the tire, a first concaved surface having a radius of R.sub.1, which extends from the outer end of the protection rib towards the tread portion, a second concaved surface having a radius of R.sub.2, which extends from the inner end of the protection rib towards the bead portion, and said radii being in a relation of R.sub.1 >

• R.sub.2, and the cross-sectional shape of the protection rib being defined by the following formulae:
• 3.0R.sub.0 >R.sub.1 >0.5R.sub.0
• 1.4.gtoreq.d.sub.1 /d.gtoreq.0.7 and
• 1.2.gtoreq.W/d.sub.1 .gtoreq.0.5
• wherein R.sub.0 is the radius of curvature of the sidewall portion located near the protection rib, R.sub.1 is the radius of the concaved surface of the protection rib, d is the thickness of the sidewall portion, d.sub.1 is the height of the protection rib, and W is the upper width of the protection rib.