Help interpreting weird Goodyear tire size?

Those tire sizes are the 'old' way of measuring them.

The 31" is the unloaded height of the tire on the stock rim a 10.5" wide tire is supposed to fit on according to the chart at Goodyear. Likely a

The 10.5" is the width of the tire at the fattest part of the sidewall again on the proper rim size.

Just a note, the sidewall width does not normally correspond exactly to the 'tread' width. I 'think' the 31x10.5 Goodyears have 'about' a

I 'know' my 33x9.5's have a 7.5" tread with the 9.5" sidewall width and the last pair of 31x10.5's I had measured 10.25" at the tread but they were MudKings, not Goodyears. Every maker is slightly different.

Our 235/75R15 BFG's measure 8.5" on the tread.

Mike

Those are Light Truck tires. 31 inches in diameter, 10.5 width at the sidewalls, R = Radial 15 inch rim width, Light Truck

If those are what was on that vehicle from the factory (check the door tag to be sure) then you almost have to buy that size. Metric sizing would be close to 325/75/15 and those are not real common.

"Steve W." wrote

Really? In my metric system, 10.5 inches is 266.7mm. That would be about a 265/75-15, or 255/80-15.