Iso uses two numbers.
Understanding bicycle tire sizes.
A third type of tire size might appear on either a mountain or a road tire.
27 iso size 630 is an older size that was used for road bikes but since so many bikes were built with this size it is still readily available.
Between 18 622 and 25 622 there are tyres of 19 20 22 and 23mm section.
Finding the right inner tube depends on the size of the tires on your bike.
However the most common 26 wheel which is denoted by 26 1 0 or 559mm bsd does not have a designated french size.
The international organization for standardization iso has upgraded a universal tire sizing method which removes this complexity.
A tire size you might see on a road bike.
29 x 2 3 indicates a tire with a 29 outer diameter and a 2 3 width.
A hybrid of road and mountain tires cyclocross tires are labeled as 700c and have widths indicated in millimeters like road bikes yet are knobbie like mountain bike tires.
Nowadays bike tires are typically marked according to iso standard a system originally developed by etrto european tire and rim technical organization but older english and french tire size dimensions are still used as well use the data from the following tables to determine interchangeability and convert between iso etrto english.
When it comes to choosing width there are two major factors at play.
23c 25c and 28c their width in mm.
The 2nd iso number is found on the diameter of the drop seat of the rim in mm.
Sizes of 26 and 24 tubulars are not well standardized.
700x25c indicates a tire with a 700mm outer diameter and a 25mm width.
The table below lists most of the sizes of tyre that are likely to be found in the uk.
Size variations of tubulars are covered in sutherland s handbook for bicycle mechanics 7th edition available from sutherland s and on the mechanic s bookshelf at better bike shops.
There are five tire diameter sizes that are in common use on modern standard adult bicycles.
There are french sizes for variants of the 26 wheel.
The first one is the width of the tire or rim in mm.
Road bike tires generally come in three widths.
Sizes written as decimals such as 2 75 are different than sizes expressed as fractions such as 2 3 4.
Where you see a block of two or more compatible sizes having the same bead diameter you can assume that intermediate sizes exist that will also fit the same rim.
The letter at the end of a tire size is a throwback to an old french system when the letters a b and c designated different inner tire diameters it does not stand for cm.
A tire size you might see on a mountain bike.
While you can find a variety of bikes with wheel sizes ranging from 16 to 27 5 inches the most common sizes include 26 inches 27 5 inches 29 inches and 700c.
With french measurements and mountain bike tires all you really need to know is that 650b 27 5 and 700c 29.
Take the rim with you when buying a tire and vice versa.
Conversion tables for common bicycle tire sizes.
