ISO 5775

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ISO 5775 is an international standard for labeling the size of bicycle tires and rims. The system used was originally developed by the European Tyre and Rim Technical Organisation (ETRTO). It is designed to make tire sizing consistent and clear. It replaces overlapping informal systems that ambiguously distinguished between sizes. For example, at least 6 different "26 inch" sizes exist (just by American notation), and "27 inch" wheels have a larger diameter than American "28 inch" (French "700C") wheels. The Japanese Industrial Standards Committee also cooperates with ISO 5775. The corresponding Japanese standards are JIS D 9112 for tires and JIS D 9421 for rims.

Part 1, addressing tyres' designations and dimensions, was last published in August 2023 and Part 2, addressing rims, was last published in March 2021.

Part 1 considers tyres' nomenclature, size designation, marking, dimensions and compatibility with different rims and rim widths.

Part 2 considers both general requirements and specific requirements for 5 sub types of rim: straight-sided, tubeless straight-sided, hooked bead, crochet type (not the same as hooked bead type), and tubeless crochet type rims.