I noticed many CX bikes back in the day (prior around 2010) came with 15C rims and had 35mm tires on them. Nowadays, these would be considered out of specs by ETRTO, some even publish more restricted ranges marking anything outside but within ETRTO as "non-optimal".
Does anyone understand how it became that universal regulatory body came to dictate these for the manufacturers rather than manufacturers defining what's permissible for their own products?
Also, what is the logic behind e.g. 35mm tire being out of spec for 15C rim, but 19C can take tire up to 62mm - more than triple?
Has the hook design changed over time (NOT talking about hook-less rims), or the tire beads or what caused the regulation to become necessary?
https://www.wtb.com/pages/tire-rim-fit-chart