Originally Posted by
Old Fat Guy
That go for cars, too?
I guess it all depends on the speed that you use the tires at.
The purpose of tread is to move water away so the rubber can grip the road. With no tread on a car, it will hydroplane at about 45 mph. This varies due to the width of the tire.
A bike tire is so narrow that I believe Sheldon Brown estimated you would need a speed of 100+ mph for one without tread to hydroplane. So again, directional treads are just plain silly.