Originally Posted by Sy Reene

Yeah, supposedly not ok per ETRTO -- but this is nothing new. People have ignored ETRTO for a long time.
As for what is officially "allowed", and getting a real read on what is ok, there's various differing info out there. eg.
Veloflex indicates an 18mm max internal width to run a 25mm tire hookless: https://www.veloflex.it/en/blog/post...-rims-coupling
Vittoria is similar: https://www.vittoria.com/ww/en/stori...rto-bike-tires

I typically refer to some charts that Mavic used to have up, but have taken down -- it marries both width compatibility with tire pressure, which makes sense. This would tell you that 21mm is the widest TSS(hookless) rim you can use for 25mm tires, but max of ~72psi.
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