Ok...hmm I'm guessing you have 7 inch wide rims (converted to mm is 178 mm) Zero offset puts you at 89mm. Now a plus 40 leaves you with 89 mm +40 mm from the inside lip of rim to mounting point (rim and rotor come together). You probably won't be able to go much bigger than 10mm spacer without changing the studs. You need 1/4 engagement of lugnut on the studs (for safety). You also need two sets of hub centering rings. 1 for the spacer to the hub center and one for the rim to the spacer. Spend the extra money and get spacers with a flange on the outside (I'll take some pics of mine to give you an idea tomorrow). 10mm spacer should put rim face more flush to fender (with that offset you really need close to 20mm). When you get ready for your rims later, you can go wider and play with the offset more and then have to start to play with camber adjustment and roll center. But this should give you a starting point. Go 10mm, you'll be happy you did. This is where I got my spacers from
http://www.projectnissan.com/s...=4650 Nice build on this product. Have had mine in for a couple of weeks... again 2 sets of hubcentric rings.. I know the feeling of doing things a step at a time.. I think price is for a pair.. i bought 25's. I think 15 may be the smallest they sell (have to be able to cover OE studs with spacer, but allows you to go wider without changing studs. .