Ute rear measurements

Quote:

That is nearly identical to my sedan, which is 73mm one side and 86mm the other.

So your total width is 75 + 140 = 215mm

The offset of the drum face is (215 / 2) - 140 = -32.5. A wheel with the opposite offset will allow you to fit the widest possible tire. +32.5 offset wheel.

If you allow 5mm clearance each side, 205 tyres might fit. However what is unknown is the actual tire section width (is it really 205mm?) and how much the suspension/body moves under cornering.

If you rolled the inside lip of the guard and gained 5mm, then a +30 offset wheel would be perfect.

This all applies if your goal is to fit the widest tire under the bodywork. If instead you want the widest rim, you can juggle the offset a little towards the outside (less offset, or use spacer).