I want to increase the overall diameter of my tires by about 2" in order to drop my highway rpms.

I'm running BFG P215/70SR 14 that I measure 25" o/a diameter.
The BFG site says these are 25.9".
I'm not sure why there's a .9" difference in measurements (the tires are still in excellent condition, so they're not worn)

Should I go with a taller 14" tire?
The tallest I can see is a 225/70R14 at 26.5"
Only 0.6" taller than mine if I go by the BFG website.
But by my measurements, they would be 1.5" taller and may work.

Am I nuts trying to get the taller tire or should I just go ahead and switch to 15"s?