Overview
ISO 4209-2:2020 - part of the ISO 4209 metric series - defines the designations, contours and critical dimensions of drop-centre (one-piece) rims for trucks and buses. The fifth edition (2020, corrected 2021) focuses on the rim geometry and fitment features necessary for safe tyre mounting and interchangeability. Tyre dimensions, designations and load ratings are covered separately in ISO 4209‑1.
Key topics and technical requirements
- Rim designation and marking: Rims are designated by nominal rim diameter code and nominal rim width code (for example, 17.5 × 5.25); flange type may be appended (e.g., K).
- Rim contours and tolerances: Detailed contour shapes and tolerances are specified for both 5° tapered and 15° tapered drop-centre rims, with diagrams and tabulated dimensions for flange, bead seats, well depth and related features.
- Rim diameters and hump circumferences: Specified rim diameters and hump circumferences for correct tyre seating and mounting are provided in tables; measurement methods and tolerances for tyre-design purposes are defined.
- Valve holes and sealing: Valve hole shapes, locations and tolerances are specified. Edges on the tyre side must be rounded or chamfered; external edges must be free of burrs. An unbroken, smooth inside surface of at least 0.75 mm or 25% of rim thickness (whichever is greater) is required to ensure adequate sealing. Specific requirements for snap‑in and clamp‑in valves and flats/concentric circular flats for high-pressure applications are included.
- Bead seat options: Optional bead seat contours (flat vs. round humps), dimensions and recommended use (notably for tubeless tyres) are described.
- Normative references and terminology: Uses ISO 3911 vocabulary and refers to ISO 4000‑2 for passenger-car rim flange contours where applicable.
Applications and who uses it
- Rim manufacturers use ISO 4209-2 to design and produce metric drop-centre rims that meet global interchangeability and safety expectations.
- Tyre manufacturers and vehicle OEMs rely on these rim contours and diameters to ensure tyre-to-rim compatibility and correct load/fitment.
- Fleet operators, maintenance workshops and service technicians use the designation and valve-hole guidance for correct replacement, mounting and servicing (including tubeless valve selection).
- Testing laboratories and regulators reference the standard for conformity assessment, safety audits and certification.
Related standards
- ISO 4209‑1 - Truck and bus tyres and rims (metric series) - Part 1: Tyres
- ISO 3911 - Wheels and rims - Vocabulary, designation and marking
- ISO 4000‑2 - Passenger car tyres and rims - Part 2: Rims
Keywords: ISO 4209-2:2020, truck and bus tyres and rims, drop-centre rims, rim contours, rim dimensions, valve holes, tubeless tyres, rim designation.
