Wheel spacers, doesn't make sense??? Options

[retrotech]

Help.
I have been on this topic prior to fitting wheels, but the numbers don't make sense. I am using 17 x 7" 993 wheels with marked off set of 55mm. I have 205 tires mounted. I want to use 215, but everyone says they won't fit.
From the beginning I thought I would need 23mm spacers, but I just tried some 1/4" spacers that were laying around and they work.
On the front with 1/4" there is slight rub on full lock, at front of tire, with 1/2" none.
On the rear with 1/4" there is a closer fit 1/4 - 3/8" at the top inside, with tons by the fender lip, that has been rolled.
With 1/2", just the reverse as above. It almost looks like I could use 215's. But how can this work with only 1/4 & 1/2" spacers.
Anyone with a similar application to advise on there spacer size?

Retro

[retrotech]

Mueller,

Thanks for your reply. If the Rev. wheel is 35mm & your rims are 40mm, doesn't that mean a 55mm wheel should have a 15 - 20mm spacer? How can mine work with a 12.7mm/1/2" or even a 1/4" 6mm?
I thought stock 911 wheel was 35mm, so that works out to 20 mm spacer? I was ready to buy 15mm on E Bay, when I discovered that would push them out too far. What am I missing here? Will a 215 tire fit?