ISO 4131:1979

Overview

ISO 4131:1979 - "Road vehicles - Dimensional codes for passenger cars" defines a standardized coding system for vehicle dimensions to support consistent vehicle data exchange and electronic processing. It applies to passenger cars (as defined in ISO 3833) and commercial vehicles derived from passenger cars. The standard assigns compact codes to three‑dimensional reference measurements, fiducial mark coordinates and both internal and external vehicle dimensions, together with defined loading conditions for measurements.

Key topics and technical requirements

• Coding system structure
  • Codes start with the prefix “ISO” followed by a capital letter denoting the dimension type: L (length), H (height), W (width), D (diameter), V (volume).
  • Numeric ranges designate internal vs external dimensions (internal: 1–99; external: 100–199).
• Three‑dimensional reference system
  • Uses zero X, Y, Z planes and parallel x, y, z planes for consistent spatial referencing.
  • Specifies how to dimension with respect to supporting surface and vehicle reference points.
• Fiducial marks and R‑Point
  • Defines fiducial marks (No. 1, No. 2, No. 3) with X, Y, Z coordinates and heights above the supporting surface under specified loading conditions.
  • Uses the manufacturer’s R‑Point (seating reference point) for many internal measurements.
• Loading conditions
  • Measurements are defined for standard loading states such as complete vehicle kerb weight, design load, and maximum authorized total weight.
• External and internal dimensional domains
  • External: overall length, height (laden/unladen), approach/departure/ramp angles, ground clearance, track, wheel spaces, turning circle.
  • Internal: R‑Point coordinates, headroom, shoulder/hip room, seat travel, pedal and steering positions, windscreen rake and related angles.
• Definitions and references
  • Aligns terminology and measurement methods with related ISO standards (e.g., ISO 3833, ISO 612, ISO 4130).

Applications and who uses it

• OEMs and vehicle designers - provide standardized dimensional data for design, CAD models and supplier communications.
• Data exchange and IT systems - enable interoperable electronic vehicle databases, parts catalogues and regulatory submissions.
• Regulatory bodies and homologation labs - use standard measurement codes for compliance, type‑approval and documentation.
• Test houses, simulation and NVH/ergonomics teams - apply consistent reference systems for human factors, crash simulation and packaging studies.
• Fleet managers and aftermarket suppliers - rely on uniform dimension data for fitment, loading and equipment specification.

Related standards

• ISO 3833 (vehicle types/definitions), ISO 4130 (3‑D reference system), ISO 612 (vehicle dimensions - terms), ISO 1176 (weights), ISO 2958 (exterior protection), ISO 3409 (measurement methods).

Keywords: ISO 4131:1979, dimensional codes for passenger cars, vehicle dimensional coding, road vehicles standard, R‑Point, fiducial marks, three‑dimensional reference system, vehicle data exchange.