Spacers & rubbing on stock
 

I've got stock suspension, and want to grab some 18" wheels. Assuming I find wheels that do not rub even on sharp turns, would adding spacers to make them flush introduce the possibility of rubbing?

Seriously doubt it. 18's on stock suspension still gives you plenty of travel. Even if your wheels poked out pass the fender you still shouldn't rub.

If you're looking for some spacers I actually just listed mine for sell this morning. Here's the thread.
http://www.ft86club.com/forums/showthread.php?t=64374

I have eibach prokit running 18x8.75 35offset w 225 40 tires. I can perfectly fit two fingers between my tire and fender, even at that I don't think there's a concern. At stock height u should be fine

Not worried too much about the diameter (as that won't change significantly with proper tires) -- it's the width/offset I'm concerned with.

Two issues, if you don't mind helping a wheel newbie out -- I'm nervous about spending $1500 on new wheels only to find I can't make tight turns or something.

First, I see people getting coilovers to make room for a larger width wheel, but I'm fully stock. Would a large enough spacer eliminate the need for coilovers?

Second, if I do put spacers on, it will obviously make the distance the wheels arc while turning larger -- which I see as more potential to rub on the walls of the wheel well when doing a sharp turn. Is there a HOWTO somewhere that explains how I'd combine wheel and tire dimensions to ensure a 100% clearance?

Damn the fitment of you wheels is great!
How's the prokit + 18s for dd?

Putting spacers on is effectively the equivalent of going with a more aggressive offset. For example, if you have 20mm spacers and you have wheels of +45mm offset, your effective offset would be +25mm. Then just go to the wheel fitment thread here on the ft86club forums to see how well the +25 mm offset will fit at stock height and with 1" drop. Obviously the real test is still in the fit test.

I am using eibach pro kit springs on stock shocks/struts with 18x8.5 ET38 fronts with 225/40/18's and 18x9.5 et 38 255/35/18 and no rubbing and no spacers.