Overview
ISO 16650:2025 specifies requirements and characteristics for round and flat bead wire used to strengthen the bead of all kinds of tyres. It replaces the 2004 edition and defines material, coating, mechanical properties, testing, delivery and marking requirements to ensure consistent performance in tyre bead reinforcement.
Key topics and technical requirements
- Scope: Applies to round wire (nominal diameters typically 0.78 mm to 3.00 mm) and flat wire used in tyre beads.
- Classification: Three tensile-strength grades - NT (normal), HT (high) and ST (super tensile).
- Tensile strength (minimum): Specified as functions of nominal diameter d (mm):
- NT-min: T = 2050 − 200·d (MPa)
- HT-min: T = 2350 − 200·d (MPa)
- ST-min: T = 2550 − 250·d (MPa)
- Mechanical properties:
- Elongation at fracture ≥ 5%
- Yield ratio (0,2 % proof strength / tensile strength) ≥ 70%
- Tests are performed on delivered material; tensile and torsion tests are specified (ref. ISO 6892-1 and ISO 7800).
- Metallic coatings: Brass, low‑tin bronze or high‑tin bronze with defined copper/tin/zinc ranges (Table 1). Alternate coatings or zinc ranges may be agreed between purchaser and supplier.
- Chemical composition of steel and cumar weight (surface finish/weight) are to be agreed between purchaser and supplier.
- Quality and inspection: Surface quality, coating thickness, adhesion testing (Annex A), straightness, residual torsion, dimensions and tolerances, welds, packaging and marking are all covered. Inspection document formats align with ISO 10474.
- Designation and ordering: Prescribed format - e.g. “Bead wire bronze‑coated ISO 16650‑HT‑1,295”. Purchaser must state quantity, delivery unit/type and inspection document.
Practical applications and users
- Primary users: tyre manufacturers, tyre component suppliers, steel wire producers and drawing plants.
- Applications: reinforcement of tyre bead cores (passenger, light truck, commercial tyres), procurement/specification of coated bead wire, quality control and incoming inspection of bead wire batches.
- Why it matters: Ensures consistent mechanical performance (tensile, yield, elongation), reliable coating adhesion and dimensional tolerances - critical for tyre assembly, safety, and lifecycle performance.
Related standards
- ISO 404 - Steel and steel products: general technical delivery requirements
- ISO 6892-1 - Metallic materials: tensile testing at room temperature
- ISO 7800 - Metallic materials: simple torsion test for wire
- ISO 10474 - Steel and steel products: inspection documents
ISO 16650:2025 is essential for specifying and procuring bead wire that meets reproducible mechanical and coating requirements for tyre bead reinforcement.