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Old 03-16-2019, 09:23 PM   #7
husker boxster
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Join Date: Sep 2006
Location: Omaha
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Welcome to the world of offset - the amt of in & out a wheel sits on the hub. You need to pay attn to wheel width and offset when replacing OEM Porsche wheels. Thankfully, there are easy ways to figure out if potential wheels will work. The 1st item is knowing what a wheel's width and offset are. On Porsche wheels, they're stamped on the wheel right next to the valve stem. Then you take the current values and the potential wheel values and enter them in this offset calculator.

https://www.1010tires.com/Tools/Wheel-Offset-Calculator

It will tell you how far in or out the new wheels will sit on the hub vs the originals. Wheels that move too far inside may bump into suspension components, while too far out may bump fender lips.

Now to your specific situation...
Factory 986 18" wheels are 7.5" & 50mm Frt, 9" & 52mm Rear
Factory 987 18" wheels are 8" / 57mm F, 9" / 43mm R

You can adjust offsets with spacers. 5 or 10mm are common (my CSS came from the factory w/ 5mm spacers). You will need longer lug bolts if you use spacers. By eyeballing the above figures, the fronts will probably work w/o potential issues. The rears will probably need a 5 or 10mm spacer.

Chances are 911 wheels will not work, unless you want to go wild with massive spacers (the fronts probably would work but rears are too wide). Some forum members have made them work with 15mm spacers, but it's really not a good idea, esp if you want to do track days.

I have seen pics of 986s with 18" Cayman S wheels on them. Don't recall if spacers were required or not, but they will work. Search 'offset' for a lot of educational material.
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