Overview
ISO 4249-2:1990, "Motorcycle tyres and rims (Code-designated series) - Part 2: Tyre load ratings," defines load- and speed-related ratings for inch code-designated motorcycle tyres. Issued by ISO/TC 31 (Tyres, rims and valves), this second edition (1990) replaces the 1983 edition and tabulates the correlation between load index and tyre load-carrying capacity, the relationship of speed symbols to speed categories, and maximum tyre load capacities including how they vary with motorcycle maximum speed.
Key topics and requirements
- Load Index to Capacity: Tabled correlation between a tyre’s load index (LI) and its tyre load-carrying capacity (TLCC). Useful when selecting tyres for a required load rating.
- Speed Symbols: Defined mapping of speed symbols to numeric speed categories (km/h). Helps ensure tyres are matched to the motorcycle’s maximum permitted speed.
- Maximum Load Capacities: Tables for maximum tyre load capacities for standard and “extra load” tyre versions (speed symbols L and P are referenced). Includes guidance on typical inflation pressures as a reference only.
- Variation with Vehicle Speed: Table that shows percentage variation of maximum load capacities according to motorcycle maximum speed - enabling permitted load adjustments when motorcycle speed differs from the load-index-associated speed.
- Service Characteristics Indication: Requirements to indicate load index and speed symbol on tyres so service and safety information is available.
- Scope limitation: Applies to inch code-designated tyre series (designation by nominal section width and nominal rim diameter in inches). It is not a metric sizing standard, but a code-designated series description.
Practical applications and users
Who uses ISO 4249-2:1990:
- Tyre manufacturers - to assign and mark load indices and speed symbols consistent with international practice.
- Motorcycle manufacturers - to specify appropriate tyre load and speed ratings for vehicle homologation and safety compliance.
- Service centers and tyre fitters - to verify tyre suitability for a motorcycle’s load and speed requirements.
- Regulators and vehicle inspectors - to check conformity of tyre markings and permitted load/speed combinations.
- Fleet operators and owners - to make informed tyre choices based on load-carrying needs and vehicle performance.
Practical benefits:
- Ensures tyres are matched to load and speed demands, improving safety and performance.
- Provides a standardized reference for tyre selection, designation and interchangeability within inch code-designated series.
Related standards
- ISO 4249-1 - Part 1: Tyres (designation and dimensions for code-designated series)
- ISO 4249-3 - Part 3: Rims
Keywords: ISO 4249-2:1990, motorcycle tyres, tyre load ratings, load index, tyre load-carrying capacity, speed symbol, maximum load capacities, inch code-designated series.
