ISO 21634:2022

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)

• ISO 37, ISO 48‑2, ISO 188, ISO 4209‑2
• ASTM D412, ASTM D573, ASTM D2240

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.