3g hemi gas mileage

Here's an example, number not exactly pertaining to you yet this will work in either direction using your rear end ratio..

Right now you have a 3.73 gear and a 28 inch tire.
You want to know what a 27 inch tire will act like compared to your 28 inch tire.

Current tire diameter = 28 inches
New tire diameter = 27 inches

28 divided by 27 = 1.037037

Current gear ratio = 3.73

1.037037 X 3.73 = 3.868148

Example: If you put on a 27" tire it will act like it has a 3.86 gear ratio compared to a vehicle that has a 28" tire and 3.73 gears.