I afraid this is getting too personal but I did not mean to imply that Peter Rawlinson confused torsional and beam stiffness but rather that you do. How would a hatch back interfere with torsional stiffness? It's behind where the torques are applied. It might very well have an effect on beam stiffness though. Now the gull wing doors did present a were a torsional stiffness problem and so the roof in their vicinity had to be beefed up.Peter Rawlinson led the chassis and suspension engineering of the Model S. (In fact, Musk is now claiming that's about all he did, despite plenty of evidence to the contrary.) I'm pretty sure he understood the difference between beam and torsional stiffness, and I'm pretty sure he knew the Model S would not have a longitudinal driveshaft. Yet he found the penalty the hatchback opening exacted on frame stiffness to be problematic enough to take steps to avoid it in the Air.