Rearend gears

Well, as you see, at the numeric number of the ratio goes up, so does your RPM to stay at the same speed. Also, to keep the abilty to run at high speeds on the Hwy. you'll need 1 of 2 things, an overdrive trans or the abilty to obtain higher RPM's from the engine.

Gas mileage will suffer with any change in a numericaly high gear ratio.