Abstract: The object of this invention is to provide a steel cord, which has ultrafine steel filaments with a diameter of 0.04-0.14 mm stranded with each other so as to reinforce a tire carcass, and a radial tire for a passenger car using the same. The steel cord includes one core filament with a diameter of 0.04-0.14 mm and 4-7 sheath filaments, each having a diameter of 0.04-0.14 mm, spirally stranded around the core filament. At this time, the steel cord has a diameter of 0.2-0.5 mm and shear strength of 25-35 kgf. Additionally, each of the sheath filaments has a smaller diameter than the core filament, and the core filament and the sheath filaments are made of the steel filaments. The radial tire includes the tire carcass provided with the steel cord and a topping sheet, and the steel cord is embedded in the topping sheet such that a rubber gauge ratio is 200-500 % and a rubber clearance ratio is 60-250 %.

Abstract: A reinforcing steel cord for rubber products, such as steel belted radial tires or conveyor belts, is disclosed. This steel cord is improved in rubber penetration and ageing adhesive force relative to the rubber material. The steel cord is formed by twisting a plurality of brass coated external element wires around a flat and spirally twisted core, with the twisted direction of the core being the same as or opposite to that of the resulting steel cord. In the steel cord, the pitch of the twisted core is set to allow the core to be twisted 0.2 to 2 times within the pitch of the cord, thus preferably forming sufficient interspaces between the core and the external wires in addition to the interspaces between the external wires.