dssur
+1y
put the car on jackstands and remove the wheels. Doing one corner at a time:
Use a jack to compress the suspension to ride height.
tie a bolt to a string and tape it inside the fender edge. Measure from the string to the mounting surface of the hub using a square (its a right angle straightedge)
Do the same for each corner.
For the fronts and rears, make sure the measurements are close, this will tell you if you boogered the measurement or one fender is closer to the rim than another.
Take the SMALLEST meaurement of all 4. This is your "frontspacing", the maximum distance from the mounting surface to the rim edge that wont hit the fender.
To get backspacing, take the width wheel you are looking at (in this case 7.5) add an inch for the beads (8.5) and subtract the frontspace. this gives you backspace.
to get offset from backspace, take the wheel width, add an inch for the beads, divide by two (in this case 4.25). Then subtract that number from the backspace. This is offset in inches. To get mm, multiply the offset in inches by 25.4, and you have offset in mm, the minimum that will tuck.