ISO 11838:1997

Overview

ISO 11838:1997 - "Motorcycle and motorcycle-rider kinematics - Vocabulary" is an ISO International Standard that defines symbols, definitions and conventions used to describe motorcycle and motorcycle‑rider motion and kinematics. Prepared by ISO/TC 22/SC 22 (Motorcycles), the standard establishes a common terminology for two‑wheeled motorcycles (as defined in ISO 3833) and the motorcycle‑rider combination. It is explicitly a vocabulary standard: it does not specify measurement methods, reporting units or accuracy requirements.

Key topics

ISO 11838 organizes terms and symbols by system and phenomenon. Major topics covered include:

• Steering system (clause 3): steer axis, steer angle, wheel steer angle, steer torque/force, steering velocity, friction and damping torques, stiffness, counter‑steering and loss of control in steering.
• Suspension system (clause 4): wheel plane/centre, fork offset, caster/caster angle, vertical wheel travel, spring/damper stroke, suspension rate, ride rate and link ratio.
• Tyres and wheels (clause 5): tyre contact centres (conventional, geometrical, effective), camber angle, tyre slip angle, slip ratio, tyre forces (vertical, lateral, longitudinal), cornering stiffness, camber stiffness, pneumatic trail, tyre lag and relaxation length, rolling resistance and associated moments (aligning torque, camber torque).
• Axis systems and kinematics (clause 6): earth‑fixed, motorcycle and tyre axis systems and component/assembly axis conventions for expressing trajectories and motions.
• Directional dynamics, motion characteristics, aerodynamics, riding postures and tests (clauses 7–11): vocabulary used to describe directional behavior, motion characteristics, aerodynamic effects on the motorcycle‑rider combination, rider postures/behaviours and test‑related terms.

Practical applications

ISO 11838 is intended to provide a unified language for anyone working with motorcycle dynamics:

• Vehicle dynamics engineers and designers use it when modelling steering, suspension and tyre behavior to ensure consistent parameter naming and interpretation.
• Simulation and modelling teams benefit from standard symbols and axis conventions for kinematic and dynamic models.
• Test laboratories and researchers use the vocabulary when reporting results, describing test procedures and comparing data.
• Tyre and suspension manufacturers, safety regulators and standards writers rely on the defined terms (e.g., cornering stiffness, relaxation length) to harmonize specifications and regulations.
• Academic authors and technical communicators adopt the standard terminology to improve clarity in papers and reports.

Related standards

ISO 11838 references other ISO documents as normative background:

• ISO 3833:1977 - Road vehicles: Types - Terms and definitions (two‑wheeled vehicles)
• ISO 6725:1981 - Dimensions of two‑wheeled mopeds and motorcycles - Terms and definitions
• ISO 6726:1988 - Mopeds and motorcycles with two wheels - Masses - Vocabulary

Using ISO 11838 helps ensure consistent, unambiguous communication in motorcycle kinematics, modelling, testing and regulation. Keywords: ISO 11838, motorcycle kinematics, motorcycle‑rider kinematics, steering system, suspension, tyre forces, axis systems, vocabulary.