Originally Posted by
Cornchips
I am, of course, googling that question at the moment, but can't seem to find a definitive answer, I hope someone here can help.
The late, great Sheldon Brown has a great resource on tire sizing systems.
https://www.sheldonbrown.com/tire-sizing.html
I agree with him and others -- the ISO/ETRTO nomenclature is easier to convey and understand, and there's no confusion. Unfortunately, the old marketing terms (like "700c") are so entrenched in the industry, we may never get away from them.