SIZE DESIGNATION

WHAT DO THE DIFFERENT SIZES MEAN?

The sizes of bicycle tires are now designated according to the European tire and rim standard ETRTO (European Tire and Rim Technical Organization). In practice, however, the older English and French names are also used.

The ETRTO size designation (e.g. 37-622) indicates the width (37 mm) and the inner diameter of the tire (622 mm). This designation is unambiguous and allows a clear assignment to the rim size.

The inch designation (e.g. 28 x 1.40) indicates the approximate outside diameter (28 inches) and the tire width (1.40 inches). There is also the inch designation in the form 28 x 1 5⁄8 x 1 3⁄8 (approximate outer diameter x tire height x tire width). The customs information is not precise and not clear. For example, diameters of 559mm (MTB), 571mm (triathlon) and 590mm (Dutch touring bikes) are all labeled 26-inch. Tires with a diameter of 622 and 635 mm are both referred to as 28 inches. Curiously, tires with an inner diameter of 630 mm are called 27 inches. These designations have their origin - and their meaning - from the times of the tire brake that acted directly onto the tire. At that time, the exact outer diameter of the wheel and tire was dictated by the brake. Depending on the tire width, there were different standards for the inner diameter. In English language areas of the world and in MTB sports, the inch designations are widespread.

The French sizing (e.g. 700 x 35C) indicates the approximate outside diameter (700mm) and tire width (35mm). The letter at the end gives an indication of the inside diameter of the tyre. In this case, the C stands for 622 mm. The French designation does not exist for all tire sizes. B, for example not used for MTB sizes in the 700 sizes.

WHAT TIRE SIZES ARE THERE?

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You should find almost every known size designation in this list. We have tried to include all size designations that are used in the market or have been used in the past. Tire sizes with a classic fractional size designation are often found on old Schwalbe tires, and sometimes even on current models if that size designation is still in common usage.

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DIFFERENCES BETWEEN 28" AND 29" INCHES

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Both tire sizes use the same inner diameter of 622 mm and can therefore theoretically be mounted on the same rims. In Europe, 28 inches is a traditional size for touring bikes. In many countries it is even the most common tire size.

Outside of Europe, the rim diameter size designation of 622 mm was rarely used. Cyclists trying to get replacement tires for a 28" touring bike in some parts of the world sometimes encountered problems finding the correct tire size. 29" was introduced in America some years ago as a new wheel size for mountain bikes. The name came about because MTB tires are more voluminous and the outside diameter is approximately 29". However, both 28” and 29” size designations are very imprecise.

A narrow 28" tire, e.g. with a tire width of 23 mm, as might be found on racing bikes, actually has an outside diameter of just over 26". With a tire width of 40 mm, it is approximately correct that the outer diameter is 28". With very wide tires of 60 mm or more, the actual outer diameter is almost 30 inches.

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WHY AIR PRESSURE IS SO IMPORTANT

The tire is only able to carry the bicycle and rider if it has sufficient air pressure. On the road, the following applies for very smooth surfaces: the higher the air pressure, the lower the tire's rolling resistance. The susceptibility to punctures is also lower at high pressure; particularly from pinch flats. Air pressure that is permanently too low often leads to premature tire wear with cracking of the sidewall being a typical result. The abrasion wear is then also unnecessarily high.

Conversely, an under-inflated tire absorbs road shocks better. Wide tires are generally used at lower inflation pressures. The larger air volume is advantageous in that it absorbs road bumps and holes, but does not necessarily suffer from higher rolling resistance, less puncture protection or tire wear. Tubeless tires can also be used at lower inflation pressure.

Our overview gives you an indication of the "right" air pressure for your bicycle tires.

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WHICH TIRES FIT ON WHICH RIM?

Tires and rims must match. More specifically, the inner diameter of the tire must match the diameter of the rim shoulder. The tire size 37-622 fits, for example, on a rim 622 x 19C. In addition, tire width and inner rim width must be matched. Our overview shows possible combinations of tire width and inner rim width according to the ETRTO.

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