I wonder if the wheels centre under load? As the power is transfered to the road?
As for the roof the new MX5 roof is fantastic, Saturday out with the boss in her MX5 nearing a junction the rain increased to ingress mode. Less than 5 seconds to put it up and lock it, while we were on the move.
My 2010 roadster has its wheels forward of centre in the arch.
I would happily have an S5 not that my wallet would accommodate one, even with the niggles I think they are stunning.