RonCT

Go-C4S - The reason 19" works "best" for the C2S / C4S is that is the wheel and tire Porsche designed for the car. Not only did the engineers work toward that wheel size, they brought Michelin and Pirelli along for the ride to modify their tires (ie: sidewall characteristics, compound, etc.). So, with 20" on the CGT, the chasis / suspension was all engineered to using that specific wheel. Of course, if you go back many years you'll find some posts by guys like me that "discovered" why they went to 19" in the first place for the 997 because we all know that 18" is the superior wheel size for performance on cars like ours. I still remember watching that first "test drive" of the 997 and 997S by the same Porsche race car driver in Japan. He lamented several times during the in-car track sessions about "why did Porsche not use the 18" wheel format for the 997S?!? It is clearly the superior setup as I'm finding right here on the track..." The Porsche marketing department trumped the engineering department. Management followed the dollars - people wanted "big" wheels and despite the engineers saying "no", they had to design the car around just that. At least they had some control over the tires.