Hydroplaning or aquaplaning by a road vehicle occurs when a layer of water builds between the rubber tires of the vehicle and the road surface, leading to the loss of traction and thus preventing the vehicle from responding to control inputs such as steering, braking or accelerating. It becomes, in effect, an unpowered and unsteered sled.
Hydroplaning also affects aircraft tires in contact with a wet runway and rollercoasters on a wet track.
http://en.wikipedia.org/wiki/Hydroplaning_(tires)
on Sheldon Brown
Even with automobiles, actual hydroplaning is very rare. It is a much more real problem for aircraft landing on wet runways. The aviation industry has studied this problem very carefully, and has come up with a general guidline as to when hydroplaning is a risk. The formula used in the aviation industry is:
Speed (in knots) = 9 X the square root of the tire pressure (in psi.)
Here’s a table calculated from this formula:
Tire Pressure Hydroplane Speed
Miles per hour Hydroplane Speed
Kilometers per hour
P.S.I. Bars
120 8.3 113 183
100 6.9 104 167
80 5.5 93 149
60 4.1 80 129
40 2.8 66 105