I posed this question a couple of weeks ago but I still can't seem to resolve it in my mind. I recently bought a new Cayman which came with the 17" wheels. The dealer has offered to swap them for 18" Cayman S wheels for $1200. I know there may be some additional weight with the larger tires but am I going to see any noticable impact on acceleration with the 2.9 engine? Any significant rougness of ride with 18" vs 17". I guess basically it boils down to an appearance issue for me in wanting the 18s. Thanks for you input.