And that is exactly where all the debate becomes interesting. I'm sure we can agree that hydroplaning only occurs on standing water. Wet asphalt is not enough.

Some engineers claim that the round shape of a bike tire makes the front of the contact patch pointed, so by virtue of it's shape it is already displacing the water to the left and right. Unlike a car tire contact patch which is a straight wall and wants to ride up on a plane like a boat on top of the water. The solution for the car is tread to evacuate the water. The same engineers claim that that the combination of that and a bikes low speed make it virtually impossible to hydroplane. The same engineers say that is why airplanes have round slick tires, to improve braking grip in dry, and prevent hydroplaning on standing water. When asked why cars don't use round profile tires they answer that by saying that a rounded profile and sidewall would be to unstable for a car when cornering, something that airplanes only do at a turtle pace and bikes negate by virtue of leaning into the corner.

Jobst Brandt had a pretty impressive engineering resume. He was also a a huge bicycle fan. I think you'd enjoy reading this if you haven't already.

Tires with Smooth Tread by Jobst Brandt