ETRO is actually the better way to talk about tire size. Most people would call that a 26" rim, but there are several variations that are all nominally called 26"; the rim size that is commonly referred to as 26" actually has an ETRO of 559mm, which specifies it exactly and causes much less confusion than calling it a 26" rim. Unfortunately, the ETRO standard has not caught on well, and the old confusing nominal terminology for tire and rim sizes still persists.