STANDARD by Deutsches Institut Fur Normung E.V. (German National Standard), 03/01/1981


Which is apparently a two page document available for $34, here: https://www.techstreet.com/standards...=1056179#jumps

I have not been able to find a free version of this document. However, without even seeing the document and just noting the date of March 1981 I'm pretty sure it's not really relevant anymore. Especially since it predates the mountain bike boom and all that came with it. Not to mention tubeless, better compounds, better aluminum and manufacturing standards.

What interesting is how the german page explains the chart
x Permitted combinations according to ETRTO
* Tire manufacturers did not call this combination technically sensible, especially not for tandems.
Flank break threatens. Who combines so, drives a time bomb. (I've always assumed "flank break" has something to do with sidewalls or the bead itself.)
Too narrow tires increase the risk of pinch holes.

What's also funny is that for a while it was warning du jour that wider tires on narrow rims would cause pinch flats but the chart seems to suggest the converse is the issue.

ETA: There were/are several 48/50/52mm mountain bike tires designed to have the side knobs in the optimal place when on a narrow rim 15-19mm wide. Both manufacturers and end users have long disregarded "the chart", IMO it's really only useful for having something to post in a thread if one is too tired to write an anecdote or cite a more modern website