ISO 5775

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).

Part 1 considers separately the cases of Clincher tires can be mounted on straight-side or crochet-type rims.

The ISO 5775-1 standard also defines procedures for measuring tires and for calculating from the marking the maximum dimensions of a tire, which are needed by designers to determine clearance distances to other bicycle components.

An example for such a marking is Part 2 defines designations for bicycle rims.

It distinguishes between Both crochet (C) and hooked-bead (HB) rims have inner profiles that curve inwards near the outside diameter of the rim to provide a hook that helps retain the tire bead under high pressure.

The tire is held in position radially by the hook without a bead seat playing a role.