Scott,
1. You and 1314 are taking my "inaccurate" statement incorrectly. Yes, it's accurate for trying to match the overall diameter of the OEM size. NOT what's optimal for the car-wheel.
2. The reality is that what the calculator suggests is not what
should be used. You think Ford or any other manufacturer puts
the optimal wheel and tire size on every car? Seriously unlikely. Ford
thought a 16" wheel was optimal for the handling and performance STOCK. We don't even know if that was why - it could be that they wanted to be cost efficient. Who knows. You've upgraded suspension right? Beefier, stiffer, etc. Upgraded speed right? Faster, more acceleration, etc. Now the vehicle is most likely better suited/can handle a bigger wheel right?
3. Your statement of "going down in tire diameter".
Happens all the time. Because people want to as you even stated "be as close to stock diameter as possible".
4. You replied with 19s are overkill. Did I say they weren't? I was refuting your point that using the calculator is the way to go. Doesn't matter WHY a 19" wheel is being put on. The point is that the calculator offers a size that would ruin the wheel. But now you're making excuses why the calculator doesn't apply because
you think 19s only belong on show cars - give me a break.
5. You also neglected to retort the commonly overlooked point of load capacity. By upgrading from 16 to 17 or 18 the calculator recommended 215/45 and 225/35 maintains stock diameter, but does not take into consideration the air cushion size and load capacity. Those sizes decreases air and load. The 225/45 and 225/40 I and many other prefer provides a little extra air and load in addition to looking better and protecting the wheel better.
6. 18s not optimal for handling?
The true test is for you finish your suspension and have it as tight as I had mine. Then to drive on the 18s for awhile and really toss it around. Then step down to a 17" wheel and tell me that the handling isn't worse. On
the SVT I stepped up and down 16-17-17 (diff tire size)-18-15-16-19-18 (diff tire size)-18. Every time I went down, the handling was definitely not as good. On a tighter suspension, the difference is more noticable. (We're talking handling here, not speed.)
7. Why don't you hit up some really high performance handling vehicle forums like Porsche and suggest to them to step down to 17s or 16s because they are better handling sized wheels than 18s.
Simple logic tells you that more sidewall = more flex. Less sidewall = less flex = better handling. I can point you to numerous articles stating that it is common for people to upgrade wheel size for better handling.
8. As I pointed out, based on the calculator, the optimal size is for 18s is 225/35-18. Have you seen that tire size on the 18" OZ Superleggera? I trust not. I've seen it and tried it. I felt it didn't provide enough width to protect the wheel. That's why I had them removed. The 225/40 gives just enough additional width and sidewall to offer more protection to the wheel. It's peace of mind to protect a $350 wheel.
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You can speed with your rubberbanded wheels that offer less wheel protection, less visually appealing, and less air/load. I'll take better wheel protection, more comfortable ride and look better doing it.
We can agree to disagree. And agree that you are in the minority in your opinion!
Seriously though, I think we've both made our points, and can let this one go now. If you want, we can take it to the track and settle it there.
Oh, and I don't care what most ran in Autox in the 50s! Just because they did it "back in the day" doesn't mean it's right!
Nah, you da man - I don't have a car for every day of the week.
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Disclaimer: These are my opinions. I'm entitled to them jsut as Scott is entitled to his just as everyone is entitled to their own. What might look like to me might be 
to someone else. Opinions are like [censored], everyones got one. 
