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.

[smrz914]

well i think he will still have to use the 1.5" spacers even if he has 7" rims for the back the lug nuts are deeper into my rear rim and I think that the distance from the back of the wheel to where the face that touches the rotor is the smae for both size rims. I could be wrong but I went outside and did a rough measurement.

The best way to see how much spacing you need is take your time and do a rough mount of the wheels. use some wood or something as a adjustable spacer. Also remember that all 914's are not created equal.