I'm running a 3/4 drop so they don't need to tuck but I don't want the roller skat look either.

LK

 

18X8 with a 5 inch bs is pretty standard.
with the 18x8.5-you gain 1/2 in width which only puts the wheel 1/8 " further out with a 5. 3/8 back space. You won't rub or stick out should be fine.


From what I have measured in the front, 6" is possible on a 18x9.5 rim without rubbing on anything. That is on a suspension with 2" hothkis.
The only thing the wheel comes close too is the front side of the upper control arm when you have the wheel fully turned.

You can go up to about 6.25 on a 20" rim due to more room on the inside of the wheel.

For the back you can really tuck a 20" but on the 18" the inside lip of the rim comes close to the caliper brake line bolt head. I wouldn'tt recomend much more than 6-6.25 B.S.

5 3/8 should give you a good look.