so i did the math and a 305/75/16 comes out to be a 34" tire (12"wide). but i know that different tires vary in size accuracy. does anyone know how accurate the BFG's are? another words, if i order me some 305/75/16 AT's are they gunna be pretty darn close to 34" tall and 12" wide? bigger? smaller?

right now im running 305/70/16 BFG AT's and they fit nice. they dont rub at all unless on some flex. but i wanna upgrade to a little taller tire but not wider and get an add-a-leaf and different torsion bars to give myself another 2" or so. yall think theyll fit just the same as my current tires?

Do you mean a 315/75R16 because as far as i can tell BFG doesn't make the tire that you are talking about. They have a 305/70R16 which is a 33.0 in. diameter and a
315/75R16 tire which is a 34.6 in. diameter tire. Both are a little over 12 in wide. Most will tell you that a 315 won't fit without a leveling kit/ lift but there are several who have done it but most will tell you that you had better like to trim to keep from rubbing parts.

oh well i didnt know they didnt make that tire size...guess i was just hoping they did. well if i think the 315/75/16's would fit if i get the add-a-leafs and the different torsion bars. i mean those two things would give me at least an inch lift i would think...and if the 315/75's are only about an inch taller than what i have now then i think itll fit the same as the 305/70's and no addleaf and torsion bars(what i have currently)

As to your original question, I think tire measurements will usually be within a quarter inch of the calculated sizes.

Pardon my uninformed meddling, but assuming the 305/70x16 would just barely fit on my LMM ... then the 315/75x16 would be just a bit too much, the hair that breaks the camel's back. It's both a half-inch taller and a half-inch wider, almost surely causing it to rub at my rocker panel. My tires are 33x12 and adding 2" on the Tbars just barely clears, in forward, barely rubs in reverse.

But from reading here, I know you'll have an easier time of it on the earlier body. Good luck.

http://www.bfgoodrichtires.com/specs/all-terrain-t-a-ko/44.html is a table listing all the sizes BFG makes in the AT/KO model along with their diameters. They show diameters which are a little less than the math would dictate. My experience is that their published diameters are accurate. I've had lots of sets of the BFG AT tires on several different trucks.