2/6/2024 0 Comments Actual bead size chart mm![]() Oddball size formerly used on some GT models. This size is currently undergoing something of a renaissance. Most 3-speeds except Schwinn department-store or juvenile 10 speedsįrench utility bikes, tandems, and loaded-touring bikes some mountain bikes. Schwinn " lightweights", older English " club" bikes 29 inch are fat tires, same rim diameter. Most newer adult bikes for road use use this size, including most road bikes and hybrids. Older road bikes, went out of fashion in the early 1980s Instructions on measuring using the circumference are below the table.Įnglish, Dutch, Chinese, Indian Rod-brake roadstersĮxcept "27 five" and rare Danish 27 x 1 1/2 It may also be helpful to take a circumference measurement to confirm that the diameter measurement was correct. For a built-up wheel, it is easier to measure the rim's circumference. If you are working with an empty rim, it is easiest to measure the diameter, but if you have a built-up wheel, the hub will get in the way of the tape measure, making it difficult to get an accurate measurement. diameter is a few millimeters smaller, so this is a 520 mm rim. ![]() 530 mm is the outside diameter, and the ISO/E.T.R.T.O. The table below gives common (and uncommon) rim sizes with the corresponding bead seat circumference dimensions. Multiplying by 25.4 gives the diameter in millimeters, 530 mm. As an example, the measured diameter of the rim shown in the photo is 20 7/8 inches, or 20.875 inches. Next you get out your pocket calculator or smartphone app, or old-school paper and pencil. ![]() If it's a millimeter or two out of round, the spokes will pull a shallow-section aluminum or steel rim into shape - not so much for a deep-section carbon-fiber rim.) Measure across a few different diameters and take the average, in case the rim isn't quite round. Slide one end of the tape back and forth along the rim until the measurement is largest. Get the largest measurement, between two points directly opposite one another. Lay your measuring tape or ruler across the rim from one side to the other. bead-seat diameter, depending on how high the rim flanges stick up above the bottom of the rim channel. The rim's diameter will generally be about 10 mm larger than the ISO/E.T.R.T.O. ![]() You can measure either the diameter or the circumference. size number and the widths are not wildly out of line.īut 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. 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 matches, it means the tire will fit on the rim. size number, if it is marked on the tire or rim. Whenever possible, you should try to match your new tire to the old tire, using the ISO/E.T.R.T.O. We have a major article on this web site explaining the different tire sizing systems. 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. We have another article which describes how to measure rims for spokes. Note: this article is about how to measure rims for tires.
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