The conflicting reports are a result of the conflicting results that different people have had over the years. There's never going to be a consensus, and the manufacturers have their own reasons for limiting to a narrow range of tire-per-wheel width recommendations. And big tire companies have their reasons for adhering religiously to them.
Small companies will still usually mount what you want on what you want it mounted to.
With 5.5 inch wide wheels you're just over the normal max that most people run (4" wider) while with a 6" wide wheel you're right there with a 10.50 tire.
The results that Rosco experienced are textbook. But that can change with the tire brand and model as well. If you have a softer tire, you can often reduce the pressure so that it's still in the safe range but does not bow out the center of the tread as much. But not always...
What is this particular Bronco used for? Daily driving around town? Long distance running on the hot highways of AZ? Long slow slogs off road in the dirt and rocks?
My example might be slightly different, since my tire and wheel sizes were slightly larger. But still with the 4" wider size scenario. I've run 11.50 wide tires on 7" wide wheels for decades on different vehicles and never had an issue of tire wear or safety (well, that is until I got my Swamper Thornbirds!)
Maybe I got lucky, but that was my experience. I always adjust air pressure for the combination though, and rarely go by any manufacturer's recommendations. Even on newer cars my air pressures are often way different from those recommended. And that's even when I'm using the recommended size tire on the stock wheels.
In your case, since your wheel width is fixed at 5.5 and your tire choice is wider than "normal" I'd say it's a try it and see what you get. I don't see any danger in it, regarding things like a tire coming off if the pressure gets low before you notice, or a tire generating more heat from the sidewall being pulled in more. I don't see belt or tread separation as an issue. Just possibly strange tire wear.
But to that end, your location dictates that you need to be more careful about how low you go with pressure when the Bronco is loaded down and you're out on the highway. The tires can heat up in that Arizona sunshine out on a high-speed highway more so than most places. Stay up above 20 (again, depending on the tire) and you're probably fine.
What tires are you looking at specifically? If you have the chance, go down to the tire store and have them pull one for you to look at. Measure the tire as it sits (un-mounted) from bead-to-bead and see what you find. i bet you're looking at very close to 5 or 6 inches anyway. perhaps less.
So I don't see it as a stress on the tire.
Are you road-racing it? High-speed desert racing or 2-track flying? If so, I'd be more diligent in tire and wheel combinations. But for normal use, I'd say you're fine other than wear. In my cases though, even tire wear was never a problem. Forty six years and counting.
Bronconut's idea of getting a slightly wider set of stock wheels is an even better idea. It's only a half an inch, but it might be enough depending on which tire you use to bypass any tread wear woes.
Paul
