RPM Calculator, actual Tire diameter question

When using a RPM calculator input 3.23 gear/ tire size 225/70/15 =27.4" at 60 mph I get an RPM of 2377.
But If you measure the tire with the weight of the car on it. The Diameter changes to about 25.5" (thats doubling the radius of the section of the tire that has the weight load).....
So 3.23 gear/tire size 225/70/15 with weight load=25.5" at 60mph I get an RPM of 2554.
So which would be more correct ? the unloaded factory diameter of 27.4"..or the weight loaded tire diameter of 25.5" ??
Just asking ??