I have a V10 ford with 4.30 gears and 245/75/16E tires. I am thinking about putting 265/75/16E tires on it. That will be one inch of total height difference, and I know that for a fact. So with one inch difference will that effectively turn my rear gear ratio into a 4.10 or something close to that. That is my question, what will my overall gearing be with the larger tires. thanks.
I realize its only 1/2 and inch on the height of the vehicle.

 

Your axle ratio remains the same, so don't get hung up on trying to figure out what the "exchange rate" is when you change tires.

Effective overall ratio changes a bit with taller tires.

Calculator here allows all variables to be changed.

https://www.novak-adapt.com/knowledge/gearing/

Their tire calculator shows 2" between the two, but TireRack shows 1.2" or so. So using a 1" difference and the above:

With the smaller tire at 30" diameter gets you 21 or 29 mph/1000 rpm in 4th/5th gear.

At 31", you get 21/30 per 1000. In other words, less than 1/2 mph per 1000 rpm in 4th.

A 4.10 puts you at 22/31 in 4th and 5th with a 30" tire, so you are correct with your initial estimate.

At 65 mph, in 5th/4th the 30" tire should run 2223/3130 rpm, the 31"er 2151/3030.