My D4 with HDC on a very steep gravel hill locked it's wheels up quite a lot. Not all at once, I think the system takes a second to realise that the car is slipping.
Once I was used to it, it was fine but a little disconcerting the first time it did it......my head was constantly doing the maths....very steep hill, ball-bearing gravel, 3 tons....STAY OFF THE BRAKES...LOL!!!!!

