@Hyperactive:
Just a quick one this time. Been here way too much today already
My thinking is that the rate of drop off would have to be different in order to get this happening where when the steering angle is 0 (almost identical slip angles at all tires then) the balance changes from push to spin. The trouble here with "isn't drop off enough by itself" is that the front tire forces would also be dropping too. Not just the rears. So to use "g" instead of lateral force with a simple tire that rises linearly, peaks at 2 degree points, then drops at constant slope to a ridiculously low value unbelievably quickly:
Tire A:
slip angle
1------------0.2g
2------------0.4g
3------------0.6g
4------------0.8g
5------------1.0g <---peak
6------------1.0g <---peak
7------------0.8g
8------------0.6g
9------------0.4g
10------------0.2g
Obviously as you've said, if the rear tires peak and go still higher in slip angle to say 8 degrees, the lateral g for the rear drops to 0.6g. But so does the front if the steering is 0 and the slip angle is the same. That's why I centered the steering. The balance hasn't changed here. Only the overall lateral acceleration of the whole car has dropped.
The argument can be made (and was in the comments section on my video), that since I straightened the steering the rear slip angles are not really the same. They're a little bit higher. That's fine. If the tires are all the same and the tire force curves were really like this the car could accelerate into the spin. That's why I said if the car was almost a neutral steer car I wouldn't be bothered so much by this. But really, this car is a strong pusher. So the tire above might be our front tire, and the rear tire force limit is higher and might look like this instead:
slip angle
1-------------0.3g
2-------------0.6g
3-------------0.9g
4-------------1.2g
5-------------1.4g <---peak
6-------------1.4g <---peak
7-------------1.2g
8-------------1.0g
9-------------0.8g
10------------0.6g
11------------0.4g
Here the slope of the drop off is the same as the front tire (0.2g per degree) while the initial part rises more quickly and peaks higher as I'm sure you'd agree is obvious from the video.
If we start out a normal turn with the fronts peaked at 5 deg and 1.0g, the rear slip angles are a little over 3 degrees to balance it at 1.0g. We can now kick the back end out with a throttle blip up to 8 degrees and it the car should still return to the original 5 and 3 degrees. This is what happens in the first part of the video.
Ok, now let's kick the car passed the peak and straighten the steering. How much slip angle difference is there between the front and rear tires? 1 degree or so? Not sure off the top of my head, but let's just call it 1 degree. If we slide the rear out to 8 degrees, the fronts are at 7 like this:
1.0g rear (8 degrees) and 0.8g front (7 degrees). Still understeer.
And if we slide the car 1 more degree:
0.8g rear (9 degrees) and 0.6g front (8 degrees). Still understeer.
And another:
0.6g rear (10 degrees) and 0.4g front (9 degrees). Still understeer.
There is in every case here the exact same balance: 0.2g per degree understeer moment, so long as we keep the steering straight and our rear slip angle is 1 degree greater than the front. So I don't think the argument really holds true. Even with a ridiculous drop off on both tires you aren't doing much to the yaw moment passed the peak.
Of course if you countersteered in a slide with these tires and kept the fronts at 5 or 6 degrees, the car would just spin faster, which is one of my other points that I think you agree with already. And of course then as the slope of the drop off increases, steering into the spin becomes more and more likely to be a better way to catch a slide. That does illustrate excessive drop off.
In my video if I had kept the front slip angles at their peaks by countersteering and the car accelerated the spin, it would have shown tire force drop off just like you said. This is why I centered the steering right away in order to show what appeared to be greatly different slopes.
I tried to do this in my sim and it was pretty tough. The front/rear tires had to be quite dramatically different after the peaks. Much more than I was expecting really. It was kind of hard to make it do what the GT did...