I have no idea what offset to get...

Im looking at getting 18x7.5" rims and I'm lowered on Tanabe Df210's on an XB. If anyone could help me out that would be awesome! Also, how do you know the tire size??

anywhere from a 42 to 35 offset and you will be fine. and thats taking your 2 inch drop into account. anything higher than 42 offset and you might need spacers. and if your asking what tire size to get i recommend 215/35 r18s. thats pretty much what everyone is running on 18s unless you want a little more tire then you could try finding 215/40s but i dont know how common those are. O_o

thanks