well the size of a spacer depends on the offset of the wheel.. most people just like their wheesl to be at least flush with the body of the car.. any farther inside and it looks like crap.. if you put it out a little past the body it gives it a "wide-body" look.. i like that but its all a matter of opinion.. id say just measure out how for you want your wheel to go, that way ur not guessing what will look good.. i have a 19X9.5 in the back with a 35mm offset and put 1 1/4" wheel adapters on and its perfectly flush with the body. it looks amazing in my opinion.. good luck!