My understanding of "hydroplaning" was a layer of liquid between a tire surface and traveled surface. I suppose all elements have a liquid state, but I'm wondering if the term is being appropriately used here.
We all understand what's being said, and I'm not trying to pull the wool over anyone's eyes (couldn't let that one just lay around begging), but isn't there a more accurate term for the loss of traction on a surface caused by loose debris - be it salt, silt, marbles - than hydroplaning?
And as far as black marks on ice - and snow, for that matter - I chip it out of the ally behind my garage every winter. Spin 'em fast enough, and tires will lose rubber on ice.