>>1653499its an European Tyre and Rim Technical Organization recommendation
tire manufacturers also provide their own crib sheets
https://www.conti-tyres.co.uk/tyre-rim-combinationsnarrow rims are common on newer MTB, so maybe its not too much of a big deal
.ps some brands of tire are just a pain to get on anyway, slightly too small and not much stretch, has to be massaged into position to make sure the bead is evenly located
others its easy with bare hands, tire just pops right into the bead
