Overview
ISO 6725:1981 - "Road vehicles - Dimensions of two-wheeled mopeds and motorcycles - Terms and definitions" provides a standardized vocabulary for the dimensional characteristics of two‑wheeled mopeds and motorcycles. It establishes clear definitions for terms such as length, width, height, wheelbase, ground clearance, turning circle and banking angle, and defines the reference planes (X, Y, Z) used to describe those dimensions.
This International Standard applies to mopeds and motorcycles as defined in ISO 3833 (excluding three‑wheeled vehicles). It is a terminology standard only: it does not prescribe measurement methods, units, required accuracy or tolerances.
Key topics
- Reference planes and general conditions
- Orthogonal coordinate system X (transverse), Y (longitudinal median plane), Z (horizontal/supporting surface).
- Reference assumptions: vehicle on horizontal support, kerb weight per ISO 6726, tyres inflated to manufacturer’s specified pressure for max load, vehicle vertical and stationary, wheels in straight-ahead position.
- Primary dimensional terms
- Length, width, height - with notes on projecting parts and exclusions (e.g., driving mirrors).
- Wheelbase, front overhang, rear overhang - locations defined relative to wheel centres and supporting surface.
- Ground clearance - lowest point within wheel space (special case for mopeds with pedals).
- Maneuverability and geometry
- Turning circle diameter and turning clearance circle diameters (largest and smallest projection circles).
- Approach angle, departure angle, ramp angle - critical for obstacle negotiation.
- Castor (trail) and castor angle - steering geometry terms.
- Residual vertical wheel clearance - suspension travel limit under load.
- Banking angle - maximal lean before tyre/part interference.
Applications and users
ISO 6725 is useful for anyone who needs consistent, unambiguous dimensional language for two‑wheeled vehicles:
- Motorcycle and moped OEMs - design specifications, internal drawings, supplier contracts.
- Homologation and regulatory engineers - type approval documentation and compliance dossiers.
- Test laboratories and certification bodies - standardized terminology for reports.
- Component and accessory manufacturers - fitment guidelines and packaging.
- Infrastructure planners, insurers, technical authors, and aftermarket vendors - consistent product descriptions, clearances, and maneuverability data.
Related standards
- ISO 3833 - Road vehicles: vehicle type definitions (applies for scope of ISO 6725).
- ISO 6726 - Two‑wheeled mopeds and motorcycles: weights - vocabulary (referred for kerb weight and load distribution).
Keywords: ISO 6725, motorcycle dimensions, moped dimensions, terms and definitions, wheelbase, ground clearance, turning circle, approach angle, castor angle, vehicle dimensional standard.
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