Once we know this true tire size, what do we do with that knowledge?
Bludgeon people with the number on Internet jeep forums?
Use it to play with online gear calculators when there's nothing good on TV?
Actually, #2 is a legitimate use, assuming one really wants to use tire diameter (calculated or measured) vs. revs per mile or the "loaded radius x 2" in that gear calculator.
Personally, I do not use the measured or published tire diameters in gear calculators - I use the published revolutions/mile
if available or a measured loaded radius at street psi x2. Using published tire diameter or "industry standard" diameter for a tire particular size is a last resort that produces inaccurate results in gear calculators that while entertaining are no closer to reality than "someplace in the ballpark." This is so because those diameters fail to take into consideration the loaded radius, which is what axle gears actually "see." [Harry Lewellyn of Coyote Enterprises often observes that airing down is like going to a lower effective axle gear ratio*.]
Other than gear calculators I cannot think of a single time in the past 50+ years that I've been driving jeeps that I needed to know the actual tire diameter in inches or mm. If I want to know if a tire fits the way I want it to I have it mounted and see for myself; I try not to rely entirely upon manufacturer's claims or internet reports that those tires on Cousin Bubba's jeep fit just fine or that its a "
real" 33, etc.
Wait, there was one time. I measured the approximate diameter of my spare on my old CJ to be sure a fugly spare tire cover that a friend wanted to give me would fit. (It wouldn't, thank goodness, so we were all able to save face.)
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* See,
https://www.coyoteents.com/stuck-in-sand/