What's up with the automatic axle drop?

[J.Random]

The issue isn't new for 1.40. I'm not even sure it's a bug. But if this is intended behaviour, I'd like to see an explanation for it.
For both games, automatic axle drop seems to work like this:
- only cargo weight matters, trailer's dry weight (tare weight) does not;
- it doesn't matter how many axles there are in total or how many of them are liftable;
- if cargo weight is below ~9 tonnes, all axles can be lifted at all times;
- if cargo weight is between ~9 and ~15 tonnes, all axles can be lifted when stationary and they will remain lifted until truck reaches the speed of about 20 km/h, when they all drop and can't be lifted on the move;
- if cargo weight is above ~15 tonnes (or 25000lb for ATS), all axles drop automatically and can't be lifted.
For the tractor unit, all of the above applies, but only for axle behind the fifth wheel (tag lift). Mid-lift chassis can lift the pusher axle at any time without any restrictions.

I recall some dev saying that there's "physics" behind automatic axle drop. Can somebody explain what kind of fizzicks is that? Or is it a bug?

Also, when you drop an axle on a mid-lift chassis while driving, truck lurches kinda aggressively. Is that an intended behaviour?

[Us3R1-2-3]

I don't know but if it's a bug then it's still there.