I forgot about turn 1 in Germany, and also spa! And your post actually made me realise why it would be happening, and it goes alongside my previous post with the bug fixing.
Your kind of right, in the way of coding and the way the car behaves over kerbs and what not. I get the "on rail" effect quite a bit, especially in Abu Dhabi. It's more about the geometry and collision of the kerbs. Take turn 1 of Hockenheim as an example. Im not 100% sure if this was the way that they made the tracks, but seeing how the cars react when hitting curbs in this way, and how I've seen it in other games and actually working on a game with similar problems, it makes sense. The concrete of the track itself, the inner green concrete of the kerb (providing it's not raised) and the grass is more than likely all one flat plane, which probably has a single collision mesh that is flat but shaped to fit the track and the grass within the barriers. The actual rumble strip kerb itself that is on the inside of the corner, will be it's own seperate model, with it's own collision modelled to match the shape and bumps of the kerb. This will then be placed ontop of the track in the correct position, to give us the kerb on the inside of the corner.
We all know that kerbs are raised off the track, sloping up at an angle before leveling out and then dropping off down the behind the kerb. The collision will match that, and if collision of a model is intersecting or sticking out from collision of something else, it can create for some odd physics...hence what we're seeing on Turn 1 at Hockenheim. So as you turn into the corner, cutting across the kerb on the first part, the wheel runs over as intended, but as theres no raised section of the kerb further inside so the wheel drops (if it has time) down to the collision of the plane below it, making contact with the flat plane again. But then it hits the 2nd part of the curb past the apex of the corner, and as it's the back of the kerb, the collision there isn't going to be anywhere near as smooth. So the wheel then hits that at speed forcing it to bounce off and spring the front of the car in the air, giving the result that many of us experience when cutting over that kerb.
To put a little more simple, the more you cut over the kerb, the more likely your going to hit the collision at the back which will send the cars nose into the air. If you barely cut the kerb, then the wheel won't have time to drop down and hit the back of the collision mesh. Now the modellers will want to replicate the kerbs on the tracks as close to real life as possible, and the programmers will want the cars to handle in a realistic but fun arcadey way. So theres immediately a conflict there in fixing the bug. The programmers won't want to change the code as it will change the handling of the cars in general, and the modellers will want to keep the kerbs to look real, and have the collision as close as possible whilst also optimising polygons. Obviously the higher the kerb, and the steeper it is, the bigger impact it's going to have on the car making it bounce more.
So the devs probably left it as it is, and hoped that people don't quite cut the corner as much. It's not good when you look at it from our perspective, but theres not a lot else that can be done to prevent it without making the car float above parts of the track with added collision mesh that doesn't match models making it look silly, especially at slow speeds.
Hopefully what I said kind of made sense, if not then I can draw up some quick pics to help explain. But thinking about it, it's a problem that is probably going to haunt gaming for a while, or at least until physics become more advanced and can fully simulate the real world in every possible calculation...which it's kind of doing anyway, just not as accurately.
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