Can you use 18" Cayenne wheels on a 986?
 

Yes.
I have had a set of Cayenne 18" 8 x 57 wheels in my junk pile for a year and last week my wife said that she wanted them on her car. I said, "No, they won't fit." I rolled a wheel over to her Boxster with a big Cayenne tire on it and showed her that it was way too big for the wheel well.

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"No" was an easy answer, but I kept thinking about it. She is tired of the 20s and wanted a change. I realized that I have an old set of 18" tires that I could mount on the Cayenne wheels just to check it out - no money lost buying a set of new tires just to experiment.

Today I took two of the wheels along with a front and rear tire to have them mounted. I had the stock sizes figuring that even though the wheels are 'square', having a slightly undersized tire in front and oversized tire in back would still balance out to similar diameters (both just under 25") and an asymmetric footprint.

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The sidewall on the fronts rises straight up from the edge of the wheel. The rears push out slightly beyond the wheel, but not to an extreme. The fit is actually much better than the 20s (which were always at the extreme edge of 'fitting'). I have a small spacer on the rears, 5mm I think, and no adjustment in the front. Plenty of clearance all around.

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Now that I know they work, I'm going to get some new tires and do both sides. This car is not tracked or driven particularly hard. The choice is purely for how my wife wants her car to look.
:cheers:

Nice! Are the Cayenne wheels significantly heavier than 18" Boxster wheels?

It looks nice. It looks like a Carrera with those wheels. :cheers:

I think your wife will find the ride more "compliant" after the change from 20" to 18" wheels.

Looks good to boot.

Just sayin'............

TO

I would think so probably different offset too.

I'm sure that they are, but in this case I'm taking off 20"x11" Rohana RC26 wheels which are a little over 60 lbs with a low profile tire on the rear (275/30ZR20 tires). The Cayenne wheels with Cayenne tires (255/55R18 AT) weigh about 58 lbs. This is not a 'Performance mod', but this particular car is not gaining weight.

That doesn't sound horrible. I think my 18 inch Lt. Alloy Carrera Boxster wheels are in the low 50lb range with stock size Michelins, and they are only a couple lbs heavier than my 17 inch Boxster S II wheels with stock size Michelins.

Those Cayenne wheels look like the Cayman S IIs that I bought. In real life my wheels are more 3-D than I expected. The rears almost concave and the fronts convex (like those Cayenne wheels, they stick out).

I went overboard, grabbing specs for wheels and tires. Going from the 17s to these 18s I lost weight in the rear and gained less than 1 lbs at the front.

This combo should weigh around 42.2 lbs front and 45.3 lbs rear. These are based on actual rim weights and the manufacturer weight for tires.... so who knows!?!

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That is a very similar look, but these Cayenne wheels are totally convex. I finally had a day off and mounted the new tires:
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Your weights are probably pretty close. I weighed my 17 inch and 18 inch sets of wheels and tires when I changed them over last weekend.

17 inch Boxster S II wheels, front with 205/50 Michelin Pilot Sport N3 tire with 12,120 miles, 39.0 lbs. Rear with 255/40 same tire and miles 44.8 lbs.

18 inch Boxster Lt. Alloy Carrera wheels, front with 225/40 Michelin Pilot Sport 4S tires with 8,850 miles, 41.6 lbs. Rears with 265/35 same tires and miles 47.0 lbs.

Hard to say how treadwear affects weight, all my tires have plenty of tread left though.