A tilting train on a non-tilt speed restriction, speeding! This is the extreme but what my point was could happen.
The Talgo 250 Hybrid has a passive tilt system. Each coach is hung at ceiling level from frames that extend upwards from the bogies. Rather like some fairground rides the body, and with it the centre of gravity, swings
outwards on a curve, making it somewhat
more likely to overturn than a non-tilting train of similar weight and dimensions. However the Talgo is very low-slung so the C of G is likely to be lower than in most other trians. But the derailment seems to have been initiated by the diesel power car, which is likely to have a much higher C of G. I'm not sure if the power car tilts anyway.
I did say that video was extreme.
So going round a left hand curve and the stock buffeting towards the right, there must be a point where it gives way and wants to leave the left rail, it may not be as low as 20 mph overspeed, but there must be a pivotal point.
Yes there is, but an active tilting system doesn't have any significant effect on the speed at which this happens. There will be a small reaction force against the outer rail from the actuators rotating the body inwards, but this is likely to be tiny compared to other forces seen in curving.
Aren't all tilts rotating around an axis? Is that not what tilting is? The main things not like riding a motorcycle is that the maximum tilt is only 8 degrees and the axis is between two sets of wheels. I do not see why this means the CoG would not move.
In a motorcycle the line of force between the wheels and the road must go through the tyre contact patches otherwise it will tip over. On a curve the rider must move the CoG inwards (in relation to the line followed by the wheels) to allow this.
A car or non-tilting train won't tip over as long as that line of force is somewhere between the left and right wheels. The C of G stays in exactly the same place relative to the wheels. With an active tilt system the axis of rotation goes through the C of G so the overall balance is not affected. You could in principle have an active tilt system that moved the C of G inwards, which would increase the overturn speed. This would need much more powerful actuators, and probably also an even smaller body profile so the upper parts of the body don't infringe the gauge on the inward side. Since the maximum speed is set by passenger comfort and is well below the overturn speed, there is no point in doing this.