Measuring Bicycle Rim Sizes
by Sheldon "ISO/E.T.R.T.O." Brown
| One measurement is worth 50 expert opinions. --Howard Sutherland |
| One measurement is worth 50 expert opinions. --Howard Sutherland |
What size tire do you need to buy for your bicycle? There are so many different tire sizes and different systems for marking tire sizes that have been used over the years that this is often a serious problem, especially for older bicycles.
I have a major article on this Website explaining the different Tire Sizing Systems. Whenever possible, you should try to match your new tire to the old tire, using the ISO/E.T.R.T.O. size number, if it is marked on the tire or rim.
If the ISO/E.T.R.T.O. size number matches, it means the tire will fit on the rim. Tires are also designated for different widths, but you can generally interchange tires of different widths as long as you match the ISO/E.T.R.T.O. size number.
But what do you do if you don't have the original tire, or if the markings are not legible? All is not lost! If you have a tape measure, you can measure the rim to determine the ISO/E.T.R.T.O. Bead Seat Diameter. You can measure either the:
Diameter
The rim's diameter will generally be 6-8 mm larger than the Bead Seat Diameter, depending on how high the rim flanges stick up above the bottom of the rim channel.If you are working with an empty rim, this is the easiest way to measure, but if you have a built up wheel, the axle will get in the way of the tape measure, making it difficult to get an accurate measurement.
Circumference
For a built-up wheel, it is easier to measure the rim's circumference by wrapping your tape measure all the way around the rim.Depending on the design of the rim and the width of your tape measure, you may or may not be able to measuer the actual bead seat part of the rim, but you should be able to get pretty close, and you can fudge a bit to allow for the way the tape fits into your particular rim.
Below is a table of common (and uncommon) rim sizes with the corresponding bead seat circumference dimensions:
| Bead Seat Circumference (Rim measurement) | Traditional Designation | ISO Bead Seat Diameter | Applications/Notes | |
|---|---|---|---|---|
| 1995 mm | 78.5 inches | 28 x 1 1/2, 700 B | 635 mm | English, Dutch, Chinese, Indian Rod-brake roadsters (Also marked F10, F25, 700 B) |
| 1979 mm | 77.9 inches | 27 x anything | 630 mm | Older road bikes, went out of fashion in the early 1980s |
| 1954 mm | 76.9 inches | 700 C, 28 x 1 5/8, 29 inch (28 x 1 1/2 F.13 Canada) | 622 mm | Most newer adult bikes for road use use this size, including most road bikes and hybrids |
| 1881 mm | 74.1 inches | 26 x 1.25, x 1.375 | 599 mm | Very Rare U.S. size, 1940s and older. Not available. |
| 1875 mm | 73.8 inches | 26 x 1 1/4 EA.1, 26 x 1 3/8 (S-6) | 597 mm | Schwinn "lightweights", Older English "club" bikes |
| 1853 mm | 73 inches | 26 x 1 3/8 (E.A.3), 650 A | 590 mm | Most 3-speeds, department-store or juvenile 10 speeds |
| 1844 mm | 72.6 inches | 700 D | 587 mm | Oddball size formerly used on some GT models. Not available. 590 mm or 584 mm tires may work. |
| 1834 mm | 72.2 inches | 650B, 26 x 1 1/2 | 584 mm | French utility bikes, tandems, and loaded-touring bikes; some older Raleigh and Schwinn mountain bikes. This size is currently undergoing something of a renaissance |
| 1793 mm | 70.6 inches | 26 x 1, 650 C | 571 mm | Triathlon, time trial, high performance road bikes for smaller riders |
| 26 x 1 3/4 | Schwinn cruisers | |||
| 1756 mm | 69.1 inches | 26 x 1.00- x 2.125 | 559 mm | Most Mountain bikes, cruisers |
| 1718 mm | 67.7 inches | 24 x 1 1/4, 24 x 1 3/8 (S-5) | 547 mm | Rare British or Schwinn Juvenile |
| 1696 mm | 66.8 inches | 24 x 1 1/8, 24 x 1 3/8 (E.5), 600 A | 540 mm | British Juvenile, most wheelchairs French 600A is actually 541 mm, close enough |
| 1633 mm | 64.3 inches | 24 x 1, 24 x 1 1/8 | 520 mm | High performance wheels for smaller riders; Terry front |
| 1593 mm | 62.7 inches | 24 x 1.5- x 2.125 | 507 mm | Juvenile mountain bikes, BMX Cruisers |
| 1539 mm | 60.6 inches | 550 A, 22 x 1 3/8 | 490 mm | European Juvenile, folding |
| 1436 mm | 56.5 inches | 22 x 1.75; x 2.125 | 457 mm | Rare juvenile size...Schwinn |
| 1417 mm | 55.8 inches | 20 x 1 1/8; x 1 1/4; x 1 3/8 | 451 mm | Juvenile lightweights, BMX for light riders, some recumbents |
| 1382 mm | 54.4 inches | 500 A | 440 mm | European Juvenile, folding |
| 1316 mm | 51.8 inches | 20 x 1 3/4 | 419 mm | Rare Schwinn juvenile |
| 1275 mm | 50.2 inches | 20 x 1.5- x 2.125 | 406 mm | Most BMX, juvenile, folders, trailers, some recumbents |
| 1225 mm | 48.2 inches | 450 A | 390 mm | European Juvenile |
| 1159 mm | 45.6 inches | 17 x 1 1/4 | 369 mm | Alex Moulton |
| 1115 mm | 43.9 inches | 18 x 1.5- x 2.125 | 355 mm | Birdy folding bikes |
| 1096 mm | 43.2 inches | 16 x 1 3/8 | 349 mm | Older Moulton, Brompton & other folders, Recumbent front, Greenspeed trikes, juvenile |
| 1068 mm | 42.1 inches | 400 A | 340 mm | European Juvenile |
| 1059 mm | 41.7 inches | 16 x 1 3/8 | 337 mm | Very Rare Mystery tire |
| 1052 mm | 41.4 inches | 16 x 1 3/8 | 335 mm | Very rare Polish juvenile |
| 996 mm | 39.2 inches | 16 x 1 3/4 | 317 mm | Rare Schwinn Juvenile |
| 958 mm | 37.7 inches | 16 x 1.75- x 2.125 | 305 mm | Juvenile, folders, trailers, some recumbents |
| 638 mm | 25.1 inches | 12 1/2 X anything. | 203 mm | Juvenile, scooters. |
| 478 mm | 18.8 inches | 10 x 2 | 152 mm | Wheelchair casters |
| 431 mm | 16.9 inches | 8 x 1 1/4 | 137 mm | Wheelchair casters |
| Anyone who cannot cope with mathematics is not fully human. At best he is a tolerable subhuman who has learned to wear shoes, bathe, and not make messes in the house. --Robert A. Heinlein |
| Accessories | Bicycles | Parts | Specials | Tools |
|---|