But I want 17 that will look like that, I don't want 18, thanksThat 15mm spacer makes more sense when looking at that pic. I almost guessed 8.5 width but the poke seemed too much. With a 8" wide he's half inch less poke then the 9" but adding a 15mm spacer puts it out .630" so it will be have .130" more poke than a 9" with no spacer assuming same offset. 38 vs 42 offset is 4mm or .157" so if runing 18x9+38 would give you .027" more poke than that pic, or virtually the same.
A 18x8+42+15 would be very similar to an 18x9+40. The 9 will poke half inch more than 8, but the offset difference will bring it back .512 so it would be .012 less poke than the picture or virtually identical but with an additional inch inboard which might not fly.