I personally wouldn't want to chance it... That's just me though. I'd be scared ****-less airing down and really flexing the tire with anything wider than a 12.50. I've heard guys going as low as 6 or 8 psi with their tires. I won't go below 16psi do to the weight of our trucks and the narrow rim. Warnings are out there for a reason, because someone somewhere has gotten into a ****ty situation by doing something outside of manufacturers recommendations. It may be fine at 40psi but go air down to 15 and hit some gnarly trails. I'm not talking mud holes. I mean trails with rocks and roots and ledges and off-camber, etc.... This is my .02 and people are gonna do what they want anyway.... Just be aware what you're getting into. You may have issues getting the tire if you tell them it's for a narrower rim. So lie and don't tell them what they're going on. But you may run into another issue when the shop won't mount them... Just sayin.