Overview
ISO 612:1978 - Road vehicles: Dimensions of motor vehicles and towed vehicles - Terms and definitions defines the vocabulary used for describing vehicle dimensions. This International Standard standardizes terms (for example vehicle length, width, height, overhangs, ground clearance, ramp/approach/departure angles, drawbar/drawgear lengths, track, wheel space, kingpin geometry, turning circles, etc.) but does not prescribe measurement methods, units, accuracy or numerical limits. ISO 612:1978 cancels and replaces ISO Recommendation R 612‑1967 and serves as a common reference for designers, regulators and manufacturers.
Key topics
- Fundamental reference plane: definition of the vehicle’s longitudinal median plane used as the basis for most dimensional terms.
- Primary dimensions: vehicle length, width, height (unladen).
- Underbody and clearance metrics: ground clearance, height of chassis above ground (commercial vehicles), vertical clearance and lift.
- Projection and axle geometry: front and rear overhang, track, wheel space, wheelbase relationships, fifth‑wheel lead, kingpin offset and inclination.
- Maneuverability angles: ramp angle, approach angle, departure angle, turning clearance circles and turning locks.
- Towing/towed‑vehicle specifics: trailer/semi‑trailer lengths (with and without drawgear), drawgear/drawbar lengths, position of towing attachment, rear tractor clearance radius and front fitting radius.
- Bodywork and cargo space: bodywork length, maximum internal dimensions (width, length, height) for commercial bodies.
- Terminology scope: clarifies exclusions (motorcycles, mopeds and certain agricultural tractors) and measurement assumptions (vehicle stationary, tyres inflated to load‑corresponding pressures, doors/windows closed).
Applications
- Establishing a consistent vocabulary for vehicle design documentation and CAD models.
- Preparing regulatory requirements, vehicle type‑approval and homologation dossiers.
- Specifying interface dimensions for coupling systems and interchangeability of trailers/semi‑trailers.
- Supporting road infrastructure design, simulation and clearance assessments.
- Harmonizing technical communication between manufacturers, test laboratories and authorities.
Who uses this standard
- Vehicle and trailer designers and engineers
- Standards writers and compliance officers
- Vehicle manufacturers and suppliers (chassis, coupling and bodybuilders)
- Regulatory authorities, homologation and certification bodies
- Transport planners and road infrastructure engineers
Related standards
ISO 612 references and complements other ISO documents such as ISO 1176 (weights vocabulary), ISO 1726 (mechanical coupling interchangeability), ISO 3833 (vehicle types and definitions), and standards on reference systems, tyres and wheels (e.g., ISO 4130, ISO 3877, ISO 3911). Use ISO 612 as the authoritative vocabulary when cross‑referencing dimensional requirements.