offset is mm from center of wheel,
+55 = 55 mm from center.
SUBTRACT spacers, eg: +55-25 = +30mm, or +15-25 = -10mm
wheels WIDTH is inside the bead, a 7" wide wheel is ~7.5" outside.
backspace IS DIFFERENT than offset.
So mine, ~18x9+25, front w/ ~5mm spacer. That has ~9.5" OUTSIDE, so you get (front) ~5-1/5" to inside bead, 4" to outside.
+55 = 55 mm from center.
SUBTRACT spacers, eg: +55-25 = +30mm, or +15-25 = -10mm
wheels WIDTH is inside the bead, a 7" wide wheel is ~7.5" outside.
backspace IS DIFFERENT than offset.
So mine, ~18x9+25, front w/ ~5mm spacer. That has ~9.5" OUTSIDE, so you get (front) ~5-1/5" to inside bead, 4" to outside.