Wow I have never seen a wheel with no dimensions cast into it...I guess there is always a first time. Right now I assume all for rims have the same part number and therefore are the same size and offset. According to the part number you have a 8.5X18 rim with an offset or ET of 47. This is what I got out of a an online offset calculator. Based on how tight my car runs with 255/35 tires in the rear if you were to go with the 255/35 rear you would need something like an 18mm spacer. For the front using a 225/40 tire you would need something like a 9mm spacer.