One piece of cycling knowledge that is supremely frustrating is tire sizing. The late Sheldon Brown
, was, undoubtedly, the foremost authority on bike tire sizing of his time, and even he had to admit that "bicycle tires come in a bewildering variety of sizes."
For tire sizes, we primarily use the The European Tyre and Rim Technical Organisation (ETRTO
) method of measurement. The ETRTO format has been adopted by the International Organization for Standardization (ISO
) and is recognized in the industry as a reliable and uniform method for tire sizing.
An ETRTO size is comprised of two millimeter measurements, separated by a hyphen: "Tire Width - Rim Diameter." A tire reading "50-406" is 50mm wide and 406mm in diameter. For convenience, we've included traditional units beside the ETRTO listings on our website.
Here's a good explanation of the difference between ETRTO, Inch and French readings
Here's a link to Sheldon Brown's own website about the trials and tribulations of tire sizing