So if I run through your math, backspace is 1/2 wheel width +offset +bead
Lets say x= bead, so in the wheel on the left 4.5 inch +2.2 inch +x = 7.2 inch. so x= 7.2 -4.5 -2.2 = 0.5 inch
for the wheel on the right 4.5 inch +1.8 inch +x = 6.8 inch. so x = 6.8 -4.5 -1.8 = 0.5 inch
The bead is 0.5 in both cases.
If the wheel offset is 56mm, the backspace must be 184mm, if the wheel offset is 45mm, the backspace must be 173mm, everything else being equal.
I never measured the Jeep wheel, so I dunno how the actual measurements compare. And the OEM wheels are 8 inch width, so the 9 inch examples above are not exactly the same, sorry about that. Below would be an 8 inch width 18 inch example closer to the OEM wheels. Oh and notice that the example tire hangs over the bead, roughly 1 inch.
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