How are bicycle tires measured

What size bicycle tire do I need?

Which tire fits which rim?

With the information on the tire, it is easy to organize a suitable replacement coat. The decisive factor for the tire size is above all the size of the existing rim. That is why it makes sense to use the ERTRO specification as a guide. It indicates the inner diameter of the tire. Depending on the tire height, the outer diameter of the tire can vary with the same inner diameter.

With a suitable inner diameter, cyclists can vary the tire height and width within a certain range. The main limiting factors here are the fork width, the distance to the mudguard and the rim width. If you want to choose a new tire with a different width or height, you should therefore seek advice from a specialist dealer as to which tires will fit the existing rim.

How do I measure the bike tire size?

The easiest and safest way to determine the size of the bicycle tire is to use the information on the old coat. If the tire is particularly worn or damaged, the information can no longer be recognized.

In such a case, the correct bicycle tire size can possibly be read off on the rim, but if nothing is to be found there, it only helps to measure it. The easiest way to do this is with a bike that is upright, for example when it is leaning against a wall. Now you can measure the distance from the wheel hub to the ground with a folding rule or metal tape measure on the front wheel. That's the radius. The outer diameter of the tire doubles as a result. The width of the tire can also be determined with a folding rule or tape measure. To do this, simply lay the folding rule flat on the tire and read the value for the widest point.

The value in inches can also be read off with a measuring tape in inches or inches. Alternatively, divide the measured centimeter value by 2.54 - 1 inch is equal to 2.54 centimeters.

The inner diameter of the tire can only be determined when the tire has been removed from the rim.

Which bicycle tube do I need?

Like the bicycle tire to the rim, the tube should also match the respective jacket. Tubeless tires are an exception, of course - i.e. tires without a tube. Tube manufacturers therefore always state which bicycle tire sizes are suitable for a tube.
It is important that the hose has the correct valve. Sclaverand, Dunlop and Autovalves have different diameters. The valve must therefore match the hole in the rim. In other words: the new hose must have the same valve as the previous hose.

How do I set my speedometer correctly?

Anyone who uses a speedometer or a bicycle computer on their bicycle must specify the correct bicycle tire size in the device's settings. The wheel circumference is required for this. Some device manufacturers include a conversion table with the device on which the tire circumference can be read from the ETRTO size specification. That's easy. However, tire pressure and the weight of the driver can influence the circumference of the tire and thus later falsify the measurement results of the device. It therefore makes sense to measure the tire circumference yourself.

It's very easy:

  • Look for a straight route and, for example, make a mark on the tire and the road with chalk. Alternatively, the valve can also be used as a tire marker.
  • Push or ride the bike until the marking is back on the ground. Also mark the spot on the road.
  • Measure the distance between the marks.

If you want to be on the safe side, you can repeat the measurement several times in order to rule out measurement errors. Then enter the determined value in the settings of the speedometer or bike computer.


The many different specifications for bicycle tire sizes are confusing. Cyclists shouldn't be unsettled by this. In most cases, the size can be read off the tire itself. With this information it is much easier to find a suitable bicycle tire. If you want to vary the tire size, it is best to seek advice from a specialist dealer.