what is the tracking

i have a 2001 s10 blazer 4x4 - i know that the rear tires are in further than the front and that is called tracking . what i want to do is find out how much and get an adapter for the rear wheels only so they extend out as far as the front . anybody out there who knows so i dont have to find out by trial and error ?

1 1/4" wheel spacers work PERFECTLY on our trucks. Makes it look a world better too. I love mine. Try to find hub-centric (no way my spelling is right, lol) as they will be stronger.