just checked and Aldermog has 4 leaf springs, it seems the S2 Roadsters do. It is interesting that John's S1 running board to road gap is similar to Aldermog and 2cm less than you measure for your Roadster. I'm not sure what this means!
Some more measurements: From the top of rear tyre to top of inside of wheel arch is 8cm, with 16" wheels and low profile tyres.
From the lower edge of wheel arch to centre of the wheel nut is 35.3cm
I can barely get 2 fingers between the bottom edge of the wheel arch and the flat of the tyre.
Peter, 66, 2016 Porsche Boxster S No longer driving Tarka, the 2014 Plus 8...