3mm spacers

Regardless of your final decision (3 vs 5 mm), make sure you also purschase and use longer wheel bolts.

[eslai]

Talk to Boothe Designs. They advertise a 4mm spacer, at least.

http://www.boothedesign.com/spacers.html

[Mike_Yi]

Ordered the 5mm spacers from Wheel Enhancement plus the longer lugs.

[70Sixter]

You did the right thing. 5mm is less that a quarter inch and is Porsche authorized increase.