wheel spacer confusion, 17" 993 wheels Options

[retrotech]

I just got my 17 x 7" 993 wheels. I was told they are a 55 mm back spacing, and I would need 20mm to make them fit
When I measure from the back side its 5 7/8 to rim edge.
I measure my 15" deep six wheel its 4 7/8 to rim edge.
20mm is about 1/2" right? It would appear I need 1" spacer.
Am I missing something? Once again, what size spacer have others used for this aplication?

thanks for your help.

[SirAndy]

1" = 2.54 cm = 0.7874" = (about) 3/4" ...

never touched those rims, so i can't say anything about how they will fit or not.

does your car have flares? rolled fenders? what size tires right now? how wide are the current rims?

a 3/4" spacer or 1" spacer requires longer studs!

the smallest bolt on adapter spacer you can fit is 1" + 1/4" flat spacer with holes for the nuts. (that's what i use in the front)
or a 1 1/2" bolt on adapter spacer, for which you don't need an additional flat spacer. (that's what i use in the rear)

(IMG:style_emoticons/default/smile.gif) Andy