ISO 18804:2021

Overview

ISO 18804:2021 - Rims for agricultural, forestry and construction machines is an international standard that specifies rim dimensions used with pneumatic tyres on agricultural, forestry and construction equipment. Published by ISO/TC 31 (Tyres, rims and valves), this second edition defines nominal rim diameter codes, specified rim diameters, rim contours, valve hole details, tolerances and measurement methods to ensure safe, interchangeable and manufacturable rims for heavy‑duty off‑road machines.

Key topics and technical requirements

• Rim diameters and codes: Nominal rim diameter codes and corresponding specified rim diameters are provided (see Table 1). Dimensions are given in millimetres and actual measurement procedures are referenced in Annex A.
• Rim contours: Detailed contours and tolerances for multiple rim types, including drop‑centre contours (W, DW, TW, DH, MW, DD), semi‑drop‑centre (multi‑piece), divided rims, flat base and full tapered bead seat rims (DWM, VF, HF, TH), and special AG 15° and other regionally recognized variants.
• Valve holes and valve seat angles: Locations and sizes of valve holes (typical diameter 15.7 mm, with optional 11.3 mm for certain small codes) and nominal valve seat angle requirements (typical 30° ± 5°, optional up to 45° with ±5° tolerance).
• Rim knurling and flange details: Specifications for knurling, flange widths, break corners and well envelopes for tyre mounting.
• Tolerances and measurement: Permitted dimensional tolerances, measurement methods, and normative references (e.g., ISO 3911 for vocabulary and marking).
• Annexes: Annex B and C list regionally recognized diameter codes and special cases for 5° and 15° drop‑centre rims.

Practical applications

ISO 18804:2021 is used to:

• Guide design and engineering of rims to ensure compatibility with agricultural and construction tyres.
• Support manufacturing and quality control by providing exact contour, diameter and tolerance specifications.
• Ensure interchangeability and safe tyre mounting across OEMs, aftermarket suppliers and fleets.
• Assist in procurement and inspection of replacement rims and wheels for tractors, harvesters, loaders and forestry machinery.
• Provide a reference for regulatory compliance, product documentation and technical drawings.

Who should use this standard

• Rim and wheel manufacturers
• Tyre manufacturers and laboratories
• Agricultural, forestry and construction equipment OEMs
• Maintenance engineers and fleet managers
• Standards bodies and procurement specialists

Related standards

• ISO 3911 - Wheels and rims for pneumatic tyres: vocabulary, designation and marking (normative reference cited in ISO 18804:2021)

Keywords: ISO 18804:2021, rim dimensions, rim contours, drop‑centre rims, valve hole diameter, agricultural rims, construction machine rims, rim diameter codes, rim knurling.