A steel cord adapted for the reinforcement of elastomers includes: a core steel filament with a diameter dc and coated with a polymer, six intermediate steel filaments with a diameter di smaller than or equal to dc, the intermediate steel filaments being twisted around the core steel filament, ten to eleven outer steel filaments with a diameter do, smaller than or equal to di wherein these outer steel filaments are twisted around the intermediate steel filaments, and the outer steel filaments are preformed in order to allow rubber penetration inside the cord. The core steel filament, the intermediate steel filaments, and the outer steel filaments all have a tensile strength of at least 2600 MPa. The cord has an outer diameter D according to the following formula: D?dc+2×di+2×do+0.1 mm, wherein all diameters are expressed in millimeters (mm).