ok from your formula, I would say if your fronts are 8.5(+40) and your rears are 10(+25), just add a 20mm spacer to the front and you'll be good. The 19x10(+25) is going to have your RIM sitting flush with the fender. And with the +20mm spacer for the front it'll put your front RIM 1mm behind the fender. B/c you are going to have a small stretch on both tires you could add a +10mm spacer to the rear and that'll put the back RIM 10mm past the fender. So then it'll look funny and you would have to do either a +25mm or +30mm to the front to make the poke of all the rims look about the same.
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