I am now including an averaged graph with results obtained yesterday with our 2015 model. The graph changes some, but there will be significant (operator-dependent) variability with such a small number of data points (n=2). The main difficulties in obtaining real-time data is making sure the road is on level plane (how does one do that without a test track or the Salt flats), and to insure speed is maintained while minimizing aggressive accelerator changes. If more can post their results, the curve will certainly become more accurate, but at least this is a start (picture 1).
Which then leads to how can our X3 become more aerodynamic, which was the impetus for this thread? If we as consumers set the cabin box dimensions for our X3 as is, then the frontal surface area will not be able to change much. I like the X3 so I can haul 1200 lbs and large items when needed (without having to have a hitch an pull a trailer). A few weeks ago we took one of our old 55" widescreen Tvs to a relative 300 miles away. We didn't have a box, and it is so thin I was concerned about laying it flat. It fit fine. Not many in this mid-size SAV category would be able to do that. So while there may be 'sportier' SAVs out there, for a true comparison, it seems one must stay on point as to interior dimensions to insure apples are being compared to apples.
So, what is in store for the G01? Looking at the aerodynamics, the only thing the designers can do is either lower our height minimally, or make it longer. I'm including a graphic (picture 2) to illustrate (please forgive the simplistic example, but it makes the point) - if we have to push the cabin box in a wind tunnel, but we have the ability to extend the front and back like an accordion and make it more angled, it becomes clear which is more aerodynamic and easier to push.
(Picture 3) includes a review of the X5's and X3's evolution in a simple table. The X5 is our big brother, so it stands to reason that changes made in its evolution will ultimately trickle down to us. As one can see, length indeed is one of the big determinates in allowing the designers to decrease frontal angles to the wind, and despite the weight increase, the HWY mpg increases.
(Picture 4) shows our X3 in a measured format and a rough idea as to how just increasing the length by 6" (leaving the cabin dimensions exactly the same), would allow the designers a chance to improve the aerodynamics. I also show if one could change it 20" (impossible, just shown for effect) how aerodynamic it would become.
(Picture 5) takes our own 2015 X3 M Sport and with some simplistic Photo-editing (apologies here), what 4" on the front end, and 2" on the back end could accomplish. As I don't have (or know anything about) modelling software, I can't say what effects those changes on the Cd would be, but by the X5's example, it must be significant. Plus, with the new 'M' variant coming, it would seem the engineers would appreciate some more room in the front for a bigger engine.
In sum, it seems even though the 'size' may not change as Scott indicated (suspecting that implies internal cabin dimensions), it seems that there must be at least some change in the length (+/- wheelbase to go along with such) if signficant Cd improvements on that 40% which deals with the body design. Our X3 appears to have the worst aerodynamic profile of any of BMW's models, and given its popularity, alot of attention must be going into improving such (beyond just the wheels, wheel wells, underbody, and air vents) for the G01 (or so I hope).