ISO 8664:2018

Overview

ISO 8664:2018 - Tyres for agricultural tractors and machines - Code-designated and service-description marked radial drive‑wheel tyres - specifies the marking, dimensions, load ratings and reference speeds for radial drive‑wheel agricultural tyres that carry a code designation plus a service description (load index and speed symbol). It applies to tyres in the 40 km/h (speed symbol A8) and 50 km/h (speed symbol B) categories and aligns tyre data needed for design, selection and homologation.

Key topics and technical requirements

• Tyre marking: mandatory elements include the tyre size designation, service description (load index and speed symbol), and optional supplementary service descriptions (shown in a circle). Tubeless tyres must be marked “TUBELESS”; an arrow may indicate preferred rotation.
• Dimensions and measurement rims: standard tyre sizes, measurement rims, design dimensions and maximum in‑service dimensions are provided (Annex A). Approved rim contours are listed (Annex C).
• Load ratings and inflation pressures: basic tyre loads and load indices with reference inflation pressures (e.g., 120, 160, 210, 250 kPa) are given in Annex B. The tyre manufacturer determines the actual pressure to use in service.
• Load/speed relationship: the standard defines how allowable tyre load varies with service speed for non high‑torque applications (see Table 1). Supplementary service descriptions may have separate load tables.
• Special applications: guidance for high and sustained torque conditions (e.g., ploughing) - loads may be increased up to 7% (consult manufacturer). Combine harvester cyclic loading permits up to 170% of basic tyre load at speeds up to 10 km/h with an approximate 30% inflation increase (manufacturer confirmation required).
• Homologation parameters: rolling circumference (RC), rolling circumference index (RCI) and speed radius index (SRI) used for vehicle speed calculations are specified (Annex D).

Applications and who uses this standard

ISO 8664:2018 is essential for:

• Tyre manufacturers - for product marking, dimensional and load data, rim compatibility, and conformity with international requirements.
• Agricultural vehicle and wheel/rim manufacturers - for chassis and clearance design, wheel strength checks and fitment specifications.
• OEMs and fleet managers - for correct tyre selection, load/speed compliance and safe operation in field and road conditions.
• Testing labs and homologation bodies - for speed/ground‑speed calculations and certification (RC/RCI/SRI).
• Agricultural equipment dealers and end users - to interpret tyre markings (load index, speed symbol, supplementary service) when specifying replacements.

Related standards

• ISO 4223‑1 (definitions), ISO 3965 and ISO 11795 (speed/ground‑speed and homologation), ISO 18805 (classification), ISO 4251‑1/‑2 (diagonal tyres), ISO 18807 (logging/forestry tyres), ISO 13442 (construction/industrial tractors).

Keywords: ISO 8664:2018, agricultural tyres, radial drive‑wheel tyres, tyre marking, load index, speed symbol, tyre load ratings, rolling circumference, measurement rims.