Choose the right tyre size
Outer tyres
There are several ways to mark the tyre size of a bicycle’s outer tyre and choosing the right tyre size can be difficult. The easiest way to find the right new tyres for your bike is to use the ETRTO number, which is based on millimetres. The first three digits indicate the width of the tyre and the next three digits the diameter. For example, 28″ 47-622 means a tyre 47 mm wide and 622 mm in diameter. When choosing a tyre, you should start by checking the size of your current tyre, which can be found on the side of the tyre.
Inch markings are not unambiguous. It is important to be careful with them because there are different sizes of tyres and rims marked with the same inch size. For example, a 26″ tyre may be 584 and 559.
Common tyre sizes
- 12″= 203 mm
- 16″ = 305 mm
- 20″ = 406 mm
- 24″ = 507 mm (children’s bicycles and jopo)
- 26″ = 559 mm (children’s bicycles and mountain bikes)
- 26″ = 584 mm (e.g. Helkama Aino and Oiva)
- 27,5″ = 584 mm (mountain bikes)
- 28″ = 622 mm (standard bikes, touring bikes and hybrids)
- 29″ = 622 mm (mountain bikes)
Inner tubes
Inner tyres use the same markings as outer tyres. The sizes of inner tubes are wider, for example 32/47-609/642 inner tubes are suitable for 32-47 mm width and 609-642 diameter outer tyres. The above size is therefore suitable for the common 28″ 47-622 tyre.
The rim can usually be fitted with tyres of different widths, the diameter is the deciding factor. For example, a 47-622 tyre can usually be replaced by a 42-622 tyre. However, when choosing tyres of different widths, the width of the rims and forks and the space under the mudguards should be taken into account, as in many cases wider tyres are also taller.
Valves
There are three types of valves. When choosing a new tube, it is advisable to buy one with the same valve as your current tube.
- SV = Presta valve
- AV = Schrader valve (also called auto-valve)
- DV = Dunlop valve (traditional quick release valve)
