How to choose your inner tube
Check all the information indicated on the sidewall of the tyre (diameter and width). For example, 26x1.90 means that the tyre is 26 inches in diameter and 1.90 inches wide.
On the tyre sidewall you will also find the dimensions in mm in ETRTO international units.
For example, 50-559 means that the tyre is 50mm wide with a 559mm internal diameter (approx. 26x2.00).