How's it any different than a 12.50 on a 7" rim? Go for it.
So, we were talking about a 10.5 on a 6" and a 12.5" on an 8" specifically.
I dont know how tires 'work' like what forces make it unsafe to run a certain width or height on a certain rim, but the way i figure it
there is a 4.5" difference between tread width and rim width. in the both cases above.
On the 6" rim, there is a 4.5" difference. 4.5" is 75% of the width of the 6" rim. Also means that the 6" rim is only 57% of the width of the actual tread width.
With the 8" rim, that 4.5" difference is only 56% of the width of the rim, so, even though you are making up the same 4.5", it's less in comparison to the overall width of the rim. And when comparing the overall width, the 8" rim is 64% of the actual wheel.
so, the ratio of "extra tread width" (4.5" in both cases) to the actual width of the rim is different.
I don't really know if that means anything, because I dont know how that acts on pressures and stresses and whatnot.
Also i figure that it would be EASIER for a tire with a taller sidewall to be mounted on a narrower rim than a tire of the same width with a shorter sidewall to be mounted on a rim of the same width (easier on the 33x10.50 to mount than a 31x10.50).
Because both of those tires have the same 4.5" to make up between tread width and rim width, but the taller sidewall has a longer distance to make up the same difference (essentially the smaller tire would have to have a steeper angle headed from the edge of the tread to the bead)
if you want to look at the tread with ratios on the 7" with a 12.5" tire, it obviously wont be the same, looks like the excess tread width makes up more than of a percentage of the actual rim width than does the 4.5" difference on a 6" wheel. Also, the wider the tread the more gently it can curve because it has more width to do so..... but i dunno dude, i didnt say it made a difference, i was asking because it's something i dont understand, or have experience in.
BF goodrich's website says for the 33x10.50 that the rim width min/max is 7" and 9" (I know we dont always follow that stuff, hell i've seen plenty of 12.50's on like 14" wide rims, ugh)
It says for the 12.50's to run between an 8.5" to 11" wide rim.
so i guess somebody running a 12.50 on a 7" is obviously the same in principle, but like i said, i dont know if the differences in the ratio of tread width to rim width make any difference.