What is flush?
Different people have different opinions. Here's mine:
"Flush" is achieving the appearance of minimal distance between the outer lip of your wheel and the outer lip of your fender without compromising alignment specs or tire width.
A lot of people are willing to leave the last part of that sentence off. I am not.
What are the variables?
In fitting wheels for flushness, the variables are:
Wheel width
Wheel offset
Tire size
Fender modfications
Ride height
Suspension alignment
We've already stated that this write up assumes you don't want to make huge sacrifices in tire width or alignment specs. More on that to come. Suffice to say we'll only be rolling fenders and sticking to a tried and true performance alignment spec.
Since this is CR.net - we're also going to assume you are running below 12" fender-to-hub ride height. Since we're also trying not to sacrifice too much performance, we're going to assume you're above 11". (The car that these specs are based on is 11.25" front, 11.75" rear)
What about fenders?
You'll have to roll the fronts and rears flat. You shouldn't need to pull fenders at all. I'm speaking from experience on an NB. NA may need a very gentle pull in the front depending on which tires you choose and how low you are.
You may choose to remove your front fender liners. However, you can probably get away with just trimming certain portions of them back with snips or a dremel. Again - depends on how low you are. The higher you ride, the less trimming you'll need.
What about alignment?
One of the benefits of sticking to the 8" +20 rule is that you can run reasonably low without being forced to run excessive negative camber in order to fit without rubbing.
For cars lower than 12",
949 Racing recommends:
Front camber: -2.8* (or as close as you can get to it)
Caster: +2.75 to +3.5*
Front total toe: 0
Rear camber : -2.5*
Front total toe: 0
That alignment will fit perfectly.
What's the wheel size?
Ready? IMO the optimal target is equivalent to an 8" wide wheel at +20mm offset. If your wheel is wider or narrower than 8" you'll have to
do the math to see which offset is a close match.
For example: A 16x8 +20 sits within 3mm of a 949 Racing 6UL in 15x9 +36. If you put a 3mm spacer on the 6UL they'll be identically "flush".
What about tires?
The answer depends on your wheel width. If you have the 8" +20 wheel a 215 is about as wide as you will fit without pulling fenders in the front. (Again - speaking from NB experience) If you have the 9" +36 wheel 225's fit fine. Using those benchmarks you should be able to calculate what will work with your desired wheels.
Keep in mind that not all tires are created equal. One tire maker's 205 may fit like another maker's 215. Do your research.
Pictures:
Here are 16x8 +20 Rota Slipstreams with 215/45 Yokohama S-Drive tires.
Here are 15x9 949 Racing 6UL's with 225/45-15 Nitto NT-01's (no 3mm spacer in these pics)
Disclaimer: YMMV - This is what worked for me. Just because you followed some of the instructions above (or think you did) does not guarantee anything. Always do the research, the math, the test fitting and everything else yourself for your own situation. Don't come crying to me (or anyone else on CR.net) if you're not happy.