- ISO 5775
ISO 5775 is an international standard for labeling the size of
bicycletires and rims. The system used was originally developed by the European Tyre and Rim Technical Organisation(ETRTO).
Wired-edge tires can be mounted on straight-side or crotchet-type rims. Such tires are designated with their "nominal width" and their "nominal rim diameter", separated by a hyphen (-). Both are measured in
millimeters. A typical example of a tire marking according to ISO 5775-1 is:
: 32-597 inflate to 400 kPa
* The first number (nominal section width) is essentially the width of the inflated tire (minus any tread).
* The second number (nominal rim diameter) is the inner diameter of the tire when it is mounted on the rim. The corresponding circumference can be measured with a suitably narrow tape inside the rim.
* The recommended inflation pressure is marked in
The standard notes that the minimum inflation pressure recommended is 300 kPa for narrow tires (25 mm section width or less), 200 kPa for other sizes in normal highway service, and 150 kPa for off-the-road service.
The inner width of the rim on which the tire is mounted should be about 65% of the tire's nominal section width for tires smaller than 30 mm and 55% for those larger.
The section height of a tire is usually identical to its section width (for tires less than 28 mm, 2.5 mm have to be added to the width to get the height). The overall diameter of the tire is then the rim diameter plus twice the tire's section height. 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.
The standard defines a set of nominal section widths for wired-edge tires and lists recommended rim widths for each:
Older markings of wired-edge tires can be converted to ISO 5775 designations with the help of the following table:
Such older markings can be appended to the ISO 5775 designation in parentheses.
Beaded-edge tires are mounted on hooked-bead rims. They are marked with an "overall diameter code" and a "nominal section-width code", separated by a cross (×). An example for such a marking is
ISO 5775-2 defines designations for bicycle rims. It distinguishes between
* Straight-side (SS) rims
* Crotchet-type (C) rims
* Hooked-bead (HB) rims
Rims are designated by their "nominal rim diameter" and their "nominal width", separated by a cross (×). Both are measured in millimeters. The rim type codes SS or HB precede the rim designation, whereas code C is appended to the nominal width. Examples:
: SS 400×20, HB 422×25, 620×13C
The nominal width of a rim is the inner width between the straight sides or beads as one can easily measure it with a caliper (see the standard for drawings and exact measurement procedures).
The standard widths of straight-side rims are:
: 18, 20, 22, 24, 27, 30.5
The standard widths of crotchet-type rims are:
: 13C, 15C, 16C, 17C, 19C, 21C, 23C, 25C
The standard widths of hooked-bead rims are:
: 20, 25, 27
The standard diameters of straight-side and crotchet-type rims are:
: 194, 203, 222, 239, 248, 251, 279, 288, 298, 305, 317, 330, 337, 340, 349, 355, 357, 369, 381, 387, 390, 400, 406, 419, 428, 432, 438, 440, 451, 484, 489, 490, 498, 501, 507, 520, 531, 534, 540, 541, 547, 559, 565, 571, 584, 590, 597, 609, 622, 630, 635, 642
The standard diameters of hooked-bead rims are:
: 270, 321, 372, 422, 459, 473, 510, 524, 560, 575, 611
ERD - Effective Rim Diameter
ERD is a measure of rim size.rim Useful for determining the appropriate spoke length. It is the distance between opposite nipple seats in the rim. The nipple seat is the surface of the rim where the nipple head sits. Because today rims come in largely varying designs, the distance from the tire seat to the nipple seat can vary significantly between rims of the same nominal (tire seat) diameter. Therefore the ERD has no fixed relationship to the ISO 5775-2 dimensions, it is an additional measure.
Spokes project 2 mm over the nipple seat when they fully engage the thread of standard 12 mm spoke nipples, thus for simplified calculation of spoke lengths the ERD usually quoted is 4 mm larger than the nipple seat diameter.
* [http://www.sheldonbrown.com/tire-sizing.html Tire Sizing] by Sheldon Brown
* [http://www.geocities.com/spokeanwheel/measure.htm Hub and Rim Measurements] by Robert Torre
*International Standard ISO 5775-1:1997, Bicycle tyres and rims — Part 1: Tyre designations and dimensions
*International Standard ISO 5775-2:1996, Bicycle tyres and rims — Part 2: Rims
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