Steel cord for reinforcing rubber article, and pneumatic tire using same

A pneumatic tire having:

• a pair of bead portions;
• a pair of sidewall portions each extending to the outside of both the bead portions in the tire radial direction;
• and a tread portion extending between both the sidewall portions, and comprising;
• a carcass composed of at least one carcass ply which toroidally extends between the pair of bead portions and reinforces each of the portions;
• and a belt composed of at least one belt layer arranged on the outside of a crown portion of the carcass in the tire radial direction, wherein
• a steel cord for reinforcing rubber articles comprising a core formed by arranging two core filaments in parallel without twisting the filaments together, and six sheath filaments twisted around the core, wherein, letting the diameter of the core filament dc (mm), the diameter of the sheath filament ds (mm) and sheath filament twist pitch p (mm), an average sheath filament interval D represented by the following Formula (I):
• D=[L−6ds{1+(L/p)2}1/2]/6 (I),
• (where L=(π+2)dc+πds) is from 25 to 80 μm is used as reinforcing members for at least one of the belt layer, and
• wherein the belt has at least three belt layers;
• the steel cord constituting the outermost belt layer of the belt is the steel cord for reinforcing rubber articles, and wherein
• the belt has a cross belt layer laminated such that cords are crossed each other sandwiching the tire equatorial plane, and the cord diameter of the steel cord constituting the cross belt is larger than the minor axis of the steel cord constituting the outermost belt layer.