backspacing

[97 2door tahoe]

i know this might sound dumb, but does anyone know the correct "backspacing" for my truck...i really dont know wut i should get for it because im getting procomp wheels and i dont know if i want 3.75 or 4in...cus the 4in is like $90 more, I have a 97 2dr.



HELP!!!!~thanks

 

[992door]

The less you have the farther they stick out