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Measuring Bicycle Rim Sizes

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by Sheldon "ISO/E.T.R.T.O." Brown
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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.

rim diagram 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 interchange tires of different widths as long as you match the ISO/E.T.R.T.O. size number and the widths are not wildly out of line.

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:

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Traditional Designation ISO Bead Seat Diameter Applications/Notes Bead Seat Circumference
(Rim measurement)
28 x 1 1/2, 700 B 635 mm English, Dutch, Chinese, Indian Rod-brake roadsters
(Also marked F10, F25, 700 B)
1995 mm 78.5 inches
27 x anything 630 mm Older road bikes, went out of fashion in the early 1980s 1979 mm 77.9 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.
1954 mm 76.9 inches
26 x 1.25, x 1.375 599 mm Very Rare U.S. size, 1940s and older. Not available. 1881 mm 74.1 inches
26 x 1 1/4 EA.1, 26 x 1 3/8 (S-6), 650 597 mm Schwinn "lightweights", Older English "club" bikes 1875 mm 73.8 inches
26 x 1 3/8 (E.A.3), 650 A 590 mm Most 3-speeds, department-store or juvenile 10 speeds 1853 mm 73 inches
700 D 587 mm Oddball size formerly used on some GT models. Not available. 590 mm or 584 mm tires may work. 1844 mm 72.6 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
1834 mm 72.2 inches
26 x 1, 650 C 571 mm Triathlon, time trial, high performance road bikes for smaller riders 1793 mm 70.6 inches
26 x 1 3/4 Schwinn cruisers
26 x 1.00- x 2.125 559 mm Most Mountain bikes, cruisers 1756 mm 69.1 inches
24 x 1 1/4, 24 x 1 3/8 (S-5) 547 mm Rare British or Schwinn Juvenile 1718 mm 67.7 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 1696 mm
24 x 1, 24 x 1 1/8 520 mm High performance wheels for smaller riders; Terry front 66.8 inches 64.3 inches
24 x 1.5- x 2.125 507 mm Juvenile mountain bikes, BMX Cruisers 1593 mm 62.7 inches
550 A, 22 x 1 3/8 490 mm European Juvenile, folding 1539 mm 60.6 inches
22 x 1.75; x 2.125 457 mm Rare juvenile size...Schwinn 1436 mm 56.5 inches
20 x 1 1/8; x 1 1/4; x 1 3/8 451 mm Juvenile lightweights, BMX for light riders, some recumbents 1417 mm 55.8 inches
500 A 440 mm European Juvenile, folding 1382 mm 54.4 inches
20 x 1 3/4 419 mm Rare Schwinn juvenile 1316 mm 51.8 inches
20 x 1.5- x 2.125 406 mm Most BMX, juvenile, folders, trailers, some recumbents 1275 mm 50.2 inches
450 A 390 mm European Juvenile 1225 mm 48.2 inches
17 x 1 1/4 369 mm Alex Moulton 1159 mm 45.6 inches
18 x 1.5- x 2.125 355 mm Birdy folding bikes 1115 mm 43.9 inches
16 x 1 3/8 349 mm Older Moulton, Brompton & other folders, Recumbent front, Greenspeed trikes, juvenile 1096 mm 43.2 inches
400 A 340 mm European Juvenile 1068 mm 42.1 inches
16 x 1 3/8 337 mm Very Rare Mystery tire 1059 mm 41.7 inches
16 x 1 3/8 335 mm Very rare Polish juvenile 1052 mm 41.4 inches
16 x 1 3/4 317 mm Rare Schwinn Juvenile 996 mm 39.2 inches
16 x 1.75- x 2.125 305 mm Juvenile, folders, trailers, some recumbents 958 mm 37.7 inches
12 1/2 X anything. 203 mm Juvenile, scooters. 638 mm 25.1 inches
10 x 2 152 mm Wheelchair casters 478 mm 18.8 inches
8 x 1 1/4 137 mm Wheelchair casters 431 mm 16.9 inches
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

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Sutherland's Rim Measuring System

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