Will a 45 offset 18x7.5 fit the xb? Im looking at 215 40 18 tires.

yes, with spacers. I am running 18x7.5 with 215-35-18's. I had to use a spacer in the rear. I went with a 20mm spacer in the rear just because I wanted the tire to be flush. you can get away with the 10mm shims from One Ton Garage to clear. in the front I have not used any spacer but I haven't lowered my box yet. no rubbing lock to lock. we'll see with it lowered.

Do the shims work for the front as well? If they do i would just use two sets of 10mm and im set. I ahve no desire to lower my car so its not an issue.

the shims are for only the rear. since you are not lowering the car 10mm in the rear should be all you need. good luck and post some pics when you are done.