for comparison, i'm running g35 rims, they're 19x8.5 and 33 offset. since the offset is measured from the center of the rim, if you want to get the same flushness as mine then you would want to compensate by getting something around 27 offset with 225 tires. you might be able to use this to help you get the right offset with your rims:
http://www.wheelsmaster.com/rt...-Tire size comparer&showRim1=1&showTire1=1&sw1=215&ar1=45&bd1=18&rd1=18&rw1=8.0&et1=45&showRim2=1&showTire2=1&sw2=165&ar2=70&bd2=13&rd2=13&rw2=5.5&et2=40&text1=&text2=
with a 7.5" rim at 27 offset, the back spacing will be at 5.3" leaving 3.6" from the bolts to the outside of the tire (using a 225 tire). that 3.6" is the same as mine with an 8.5" rim at 33 offset using a 245 tire. if you're running a 7.5" rim i wouldn't go with 245 tires.