Not sure. I have them on steel rims on my motorbike and have yet to squish the rim even on doing a baby endo. On my mountain bike/cruiser hybrid I have some old school Araya box rims, I have actually been tossed on that bike while doing a single track and the rim was fine. That is alloy I believe. I could imagine some of the lighter rims out today could get squished, though I never ride the bleeding edge as if I want to shave pounds off my bike I could start with my stomach.