While I still believe its an ESP/ABS problem, one other thing that has come to mind is aerodynamics. Around the year 2000 Audi launched the TT and there were 5 deaths before Audi acknowledged that it had to modify the car with a rear spoiler. The accidents were in similar cirumstances as the one I have described, driving fast around bends on German Autobahns.
Audi Offers TT Fix After 5 Deaths
I think aerodynamic forces could well be part of it. They all (lift and drag) go as velocity squared. I doubt the algorithm for the rear wheel ABS has it factored properly.
I have not seen the actual flow over the vehicle, but did see a picture of one prototype with dining room table leaf sized spoilers coming off the deck lid...
Imgur
Here is speculation:
1) Pressure forces on a car can be estimated by the "streamline curvature" method. This means if you look streamlines of the actual airflow, the flow curves toward low pressure - low pressure is why it bends.
2) For cars that close the wake on a horizontal line, headroom for rear passengers conflicts with low drag and a closed wake. Chrysler 200 was notoriously canceled for compromising rear seat passenger egress.
“'The 200 failed because somebody thought that the rear-seat entry point inside the 200 — which is our fault, by the way — is not up to snuff,' Marchionne said.
The problem: The slope of the roof crimps the entry portal."
Chrysler 200: Why This Car Has Been Called a Failure
For the Model 3, different than the TT BTW, the steepest part of the pressure recovery region is pushed toward the back of the car to provide headroom. Even with the glass roof headroom and aero is a struggle.
3) If the pressure recovery region is too steep, attached flow can be intermittent. Bigger spoilers can suck down the flow to make attached flow less intermittent. "Spoiler" may be used incorrectly here... Rather let's say a fence that keeps separated/reverse flow from creeping forward off the rear face of the car. See picture of table leaf above. Dagger boards sailboats sometimes have special rear edge treatments to avoid flutter and humming - rear edge treatments are known to help stabilize the flow.
Since at high speeds the forces are high, intermittent aerodynamic lift could mess with the electronic stability control algorithm. As the car dives or rotates forward on initial braking the flow may more completely attach, changing lift suddenly. In other words, initiating braking changes the angle of attack.
In other words, you might be onto something!
Thanks for speaking up to get this resolved quickly.
I like the idea of more downforce back there by using a real spoiler - even it hurts range a bit.
