No obligation to mention the fact that the odo will record fewer miles than you actually travel. All the odo really records is the number of revolutions that the driveline has made, which is what is relevant as far as component wear and lifespan. How far the vehicle actually travels across the landscape as a result of those driveline revolutions is completely irrelevant.
255/65R16 has a circumference of 91.27 inches.
265/70R16 has a circumference of 96.14 inches.
265/75R16 has a circumference of 99.42 inches.
Dividing them you get a 5.3% difference for the 265/70s, and an 8.9% difference for the 265/75s.
However, your speedometer probably reads a bit fast with the stock tires, so your actual difference will probably be less.
Brent
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