OEM deals only in offset, backspace can be calculated or will need to be measured on an actual wheel.
In the post above yours, the picture provides the dimensions - "IS48" means wheel offset of +48mm
. - wheel mounting surface is 48mm toward the outboard edge of the wheel from lateral center
Assume wheel is 9.5" lip-to-lip (for 8.5" bead width) - 9.5 = 241.3mm
Lateral center (zero offset) of wheel is 4.75" = 120.65mm
Add 48 to 120.65 for the hub flange position of the wheel = 168.65 (from inboard edge of wheel), which is the backspace dimension - 6.64"