International Standards Organisation (ISO) Rim Sizing
The ISO number is actually the bead seat diameter. This number is usually shown on the tyre wall preceded by the tyre width in mm.
| Original Size | Typical Designation | Typical Application | ISO Size |
| 27" | 27 x 1 /14" | 10 Speed | 630 |
| 700C | 700 x 25c | Road Bike | 622 |
| 26" | 26 x 1 3/8" | Schwinn | 597 |
| 650a | 650 x 28a | 3 Speed | 590 |
| 650b | 650 x 28b | Tandem | 584 |
| 650c | 650 x 20c | Triathalon | 571 |
| 26" | 26 x 1.5 | MTB | 559 |
| 600a/24" | 600x25a, 24x1 3/8" | Kingcycle | 540 |
| 24" | 24 x 1 | V-Rex | 520 |
| 22" | 501 | ||
| 550a | 550 x 28a | 490 | |
| 20" | 20 x 1 3/8" | Ross Bike | 451 |
| 500a | 500 x 28a | Peer Gynt | 440 |
| 20" | 20 x 1.5 | Greenspeed, PDQ, BMX | 406 |
| 450a | Italian | 400 | |
| 18" | 18 x 1 3/8" | British | 399 |
| 450a | 450 x 28a | Kingcycle | 390 |
| 17" | 17 x 1 1/4" | Moulton, Lightning | 369 |
| 16" | 16 x 1 3/8" | Vision, Brompton | 349 |
| 400a | 400 x 47a | 340 | |
| 16" | 16 x 1.75 | BikeE | 305 |
| 14" | 14 x 1 3/8 | Bickerton | 298 |
| 350a | 350 x 37a | 290 |
(courtesy of Recumbent UK magazine)
| RCO |