A steel filament (122) is crimped in a wavy form or zigzag form, and the tension characteristic of the crimped steel filament (122) satisfying: for a load which is 20% of the breaking load, the elongation must be greater than 40% of the maximum elongation; for a load which is 80% of the breaking load, the elongation must be less than 90% of the maximum elongation. A cap ply strip (120) comprises more than one crimped steel filament (122) embedded more or less parallel to one another within an elastomeric matrix (124). A cap ply structure (118) comprises the cap ply strip (120) spirally and continuously wound in a tire circumferential direction above the belt structure (116). A pneumatic radial tire (110) comprises the cap ply structure (116) disposed radially inward of and adjacent to the tread (114) and radially outward of and adjacent to the belt structure (116). The crimped steel filament (122), the cap ply strip (120), and the cap ply structure (116) can not only bind the belt ply but also accommodate the blowup process for the green tire.