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These are just a few of the many standard sizes that are available for picture frames. There are lots more and the size appropriate for you will depend on the dimensions and proportions of the artwork that you want to frame. Some rims are also now marked according to ISO with their bead diameter and internal section (width where the tyre fits); 622-17 for the size usually fitted to touring and hybrid bikes, for instance. But some manufacturers give the overall width instead. Subtract 6mm from overall width to estimate the rim section, or simply measure the distance between the flanges. Starting with the ones digit of the bottom number, the multiplier, multiply it by the last digit in the top number A very popular set of standard sizes in the UK are the "A" series of paper sizes, such as A4 or A2. We have a handy guide all about "A" paper sizes too. Custom Sizes All tyres are marked with a pressure. Sometimes this is an absolute maximum that nobody should need to exceed, or sometimes only a recommended maximum that may be exceeded by heavier riders (such as tandemists).
One way to define it, popular in times past, was to measure the tyre’s outside diameter and its maximum width when inflated, but this can be misleading. For example, some tyres marked 28" are actually much less than 27 inches in diameter, while 26×1.5 and 26×1½ are two completely different sizes. That’s how the diameter and circumference (circ – equals distance rolled in one turn of the wheel) are calculated in the Tyre size table. These figures are useful for setting your cycle-computer and precisely calculating gears.Arrange the numbers one on top of the other and line up the place values in columns. The number with the most digits is usually placed on top as the multiplicand. Sometimes you can’t find any ISO size on a tyre, only the old-school markings. Although they’re familiar they can be confusing. Tyres of the same size may come with lots of different markings: 28×1¼×15/8, 28×1¾×1¼ or 700×32C, for example, which are all 32-622.
Another reason not to exceed the 2.2 limit on road is that a more bulbous tyre can deflect side ways with a noticeable effect on control and road holding. Conversely, fitting a tyre of less than 1.4 times the rim section will result in a harsh ride and more rolling drag than a larger tyre at the same pressure. Tubeless tyres
As far as possible, then, use these columns to convert to ISO dimensions and then have nothing more to do with those old markings! Tubeless tyres, as the name suggests, do away with an inner tube and, in its absence, are reliant on the shape and tightness of the tyre bead to ensure the tyre doesn’t blow off the rim at high inflation pressures; in a conventional clincher tyre, the inner tube keeps the bead securely located under the rim hook. The ideal relationship between tyre and rim section is about 1.8 to 1, but any tyre from 1.4 to 2.2 times should fit – always provided that the bead diameters correspond.
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