Overview
ISO 21634:2022 - Rubber flaps for tyres: Requirements and test methods specifies material, dimensional, performance and marking requirements for rubber flaps used with tube-type tyres on road vehicles. The standard ensures flaps protect inner tubes from rim- or tyre-caused damage, and it defines test methods to verify durability and fit. (Annex E gives requirements for non‑road tyres.)
Key topics and technical requirements
- Scope and applicability: Tube‑type tyres for road vehicles (excludes 2/3‑wheelers and non‑road tyres; see Annex E for off‑the‑road requirements).
- Materials & construction: Endless flaps made from suitable natural or synthetic rubber compounds; free from flaws and sized to fit tyre/rim/tube combinations.
- Dimensional controls:
- Inside diameter must be greater than the nominal rim diameter and less than nominal rim diameter + 25 mm (measured on rim‑side surface).
- Valve hole provided (minimum ~12 mm) located centrally unless for off‑centre rims; extra reinforcement allowed around valve hole.
- Minimum flap widths and flap‑width codes defined in Annex A; indicative thicknesses for light trucks and trucks/buses in Annex D.
- Designation & marking:
- Designation includes nominal rim diameter code and flap‑width code (or real width in mm).
- Permanent markings required: manufacturer, flap size or applicable tyre/rim sizes, manufacture month/year (Annex C), and country of origin.
- Physical tests & performance:
- Tensile strength & elongation: test per ISO 37 (alternatives ASTM D412/DIN 53504 permitted); minimum elongation at break ~275% and minimum tensile strength ~6.0 N/mm².
- Hardness: measured per ISO 48‑2 or ASTM D2240; target ~55 ± 10 Shore A.
- Ageing (heat resistance): oven ageing per ISO 188 or ASTM D573 (100 °C ±2 °C, 24 h); post‑ageing limits on hardness, tensile and elongation are specified (e.g., hardness ±15 Shore A, tensile ±30%, elongation −50% to +15%).
- Joint tensile strength: overlap joints tested per Annex B; minimum joint strength ~1 N/mm.
- Test procedures: Detailed specimen preparation, conditioning and test rates specified (see Clause 6 and Annex B).
Applications and who uses this standard
- Tyre and flap manufacturers: design, produce and certify rubber flaps to ensure proper fit and tube protection.
- Rim and wheel designers / OEMs: verify compatibility of tyre/rim/flap combinations.
- Testing laboratories & quality assurance: perform tensile, hardness and ageing tests per referenced methods.
- Regulators, fleet operators and aftermarket suppliers: ensure safety and compliance of replacement flaps.
Related standards (normative references)
Keywords: ISO 21634:2022, rubber flaps, tyre flaps, tube‑type tyres, test methods, flap‑width codes, joint tensile strength, hardness, ageing tests, tyre rim compatibility.