[OttawaSteve]

The only thing that I can see missing is sidewall height for pothole resistance, which may or may not be a consideration depending upon the condition of the roads that you drive on. Someone can correct me if I am wrong but I have never seen definitive evidence of noticeable performance gains related to sidewall height.

The main reason people get "dubs" is aesthetics - many think that more wheel and less tire looks better. My car came with 20's. Right now it has 18's with my winter tires. I like the look of both.

The other factor is Porsche - the wheel diameter generally goes up with the price. Base Box/Cay get 18, S get 19 and GTS get 20.

 

[OttawaSteve]

Here is a pic of my Cayman with the winter wheels set (18" Boxster wheels). I have the stock suspension.

 

[OttawaSteve]

Re: pros and cons of 20" vs 19" vs 18"

I've got another question. My 2014 Cayman S came with 20" wheels and OEM Pirelli tires. When pulling out of the dealer's parking lot the front end had a "bumping" sound at low speed with a hard angle turn. Similar to pulling out of your driveway to get into the road. I was told by the dealer that the bump or clunk was normal and nothing to be concerned about. Once the car is up to speed the front end noise disappears. However, I took my car into a tire dealership to order some new tires and the serviceman told me that this front end noise was odd and that I should get it checked out. Anyone else know what I'm talking about?

Look up Ackermann effect. It's been discussed many, many times on P9.