Pneumatic radial tires

Claim 1

A pneumatic radial tire constructed to reduce breaker interlayer shearing strain, comprising: a pair of bead portions; a side portion arranged adjacent to each bead portion; an outwardly convex crown having shoulder portions connected to respective side portions, a carcass composed of at least one inextensible cord layer extending across said two bead portions and aligned in a substantially radial direction of the tire, and a breaker disposed outside said carcass in said crown and having a width substantially equal to a width of said crown, said breaker comprising at least two layers of cords having a modulus of at least 10×10 3 kg/mm 2 , said breaker cords being inclined a maximum of 25° with respect to the peripheral center line of the tire in different directions between said layers, said tire having an initial sectional shape which satisfies the following conditions when spaces between said bead portions are held in a normal distance before and after pressurizing said tire: 1. R 1 /R 1 ' ≦ 0.8, 2. r 2 /w/r 2 '/w' ≧ 1.5, where R 1 is a radius of curvature of the outer profile of the carcass in a vertical center section through the rotational axis of the tire on a normal line to the outer curved surface through a width-wise end of said crown before the inside of the tire is pressurized, R 1 ' is its corresponding radius of curvature after the inside of the tire has normally been pressurized, R 2 is a radius of curvature of the outer profile of the crown in the vertical center section through the rotational axis of the tire before the inside of the tire is pressurized, R 2 ' is its corresponding radius of curvature after the inside of the tire has normally been pressurized, W is the maximum width of the tire in the vertical center section through the rotational axis of the tire before the inside of the tire is pressurized, and W' is its corresponding maximum width of the tire after the inside of the tire has normally been pressurized.