I remember reading a Sheldon Brown article on how it is impossible to hydroplane on a bicycle. I think he had calculations and all, which were meaningless to me. One experience in a lot of years of riding convinced me that hydroplaning on a bicycle is indeed possible, calculations or no. On a self-contained tour on a tandem, we were descending a mountain pass in the rain and the bike was moving all over the place. I yelled at my stoker to sit still. She said she was. I felt I had next to zero control over the bike. Of course, I never did tell my stoker that. It is the only time I have ever experienced anything like that and it was years ago. So, I've often wondered, if hydroplaning on a bike is impossible, what was I doing? It was not a shimmy. It was very much a floating sensation. I'm thinking we were on 27x1-1/4 Schwinn Le Tours and guessing we might have been in the 30-40 mph range but, it was a long time ago and we had no speedometer.