Tyre outer diameter
Tyres are differentiated according to the wheel diameter measured in inches or millimeters (ETRTO - European Tyre and Rim Technical Organisation). The bicycle tyres are usually manufactured in the range of 10 to 29 inches. They may also have different widths, the resulting dimensions being expressed in the format of 26" x 2.1" or 54-559, i.e., tyre diameters of 26" with a width of 2.1" and 559 mm and 54 mm, respectively.
When choosing a new tyre, it is worth to look for dimensions of the original. The width can be changed - in case you choose a tighter variant, it should be no problem in most cases. If you want to buy a wider maturity, carefully measure whether the mantle passes through the frame and the fork.
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Mountain bike tyres usually have a diameter of 26", 27.5" and 29". They usually have a width of 1.75" to 2.4". There are also extremes like a width of 1", which are intended only for roads or 2.6" for downhill. Again, the wider the mantle is, the more difficult terrain you will pass.
The narrower the jacket is, the more it is suitable for asphalt roads or cycle paths. Tyres with a width of 1.75 to 1.9 have a smaller tread profile and smoother tread, thus reducing the rolling resistance and allowing a faster ride. The widths of 1.9" have a pattern with perforation, so it is easier to drive in the mud, on the roots or unpaved roads.
Cross tyres
For crossbikes, tyres with a diameter of 28"/622 mm are often used, the width of which is usually in the range of 32 to 54 mm, and crossbars are particularly suitable for driving on asphalted and fixed routes caused by the smoother tyre pattern Tyre material is usually harder to allow for a faster ride and less wear on the material.
Road tyres
A 28" diameter is common in racing bikes as well as crossbikes, but the tyres are narrower (19-28 mm), with a smooth or very fine pattern.
