The tread, grooves, or sipes of a rubber tire are designed to remove water from beneath the tire, providing high friction with the road surface even in wet conditions. Hydroplaning occurs when a tire encounters more water than it can dissipate. Water pressure in front of the wheel forces a wedge of water under the leading edge of the tire, causing it to lift from the road. The tire then skates on a sheet of water with little, if any, direct road contact, resulting in loss of control.
If multiple tires hydroplane, the vehicle may lose directional control and slide until it either collides with an obstacle, or slows enough that one or more tires contact the road again and friction is regained.
The likelihood of hydroplaning increases with the speed of the vehicle and the depth of the water. Tread wear and underinflation also increase the risk for hydroplaning, as do wider tires. Narrower tires are less vulnerable to hydroplaning because the vehicle weight is distributed over a smaller rubber contact patch, resulting in a greater ability for the tires to press water to the sides, allowing tire contact with pavement.
The practice of plus sizing by replacing a vehicle's original equipment wheel size with a larger diameter wheel and replacing the tire with a lower-aspect-ratio tire of the same diameter affects, some of the performance characteristics of vehicles, as well as increases the risk of hydroplaning with the wider tires.
Bicycles, motorcycles, and similar vehicles with a round-shaped surface toward the pavement are far less likely to hydroplane in normal road use. The contact area with the road is a canoe-shaped patch that effectively squeezes water out of the way. However, because road friction is reduced in wet conditions, the lateral force that the tires can accommodate before sliding is greatly diminished. While a slide in a four-wheeled vehicle is correctable with practice, the same slide on a motorcycle will generally cause the rider to fall, with severe consequences. Thus, despite the relative lack of hydroplaning danger, motorcycle riders must be even more cautious because overall traction is reduced by wet roadways.
See also traction for effects similar to hydroplaning.
If the vehicle is traveling straight, it may begin to feel slightly loose. If there was a high level of road feel in normal conditions, it may suddenly diminish. Small correctional control inputs will be ignored by the vehicle.
If the drive wheels hydroplane, there may be a sudden audible rise in engine RPM and indicated speed as they begin to spin. In a broad highway turn, if the front wheels lose traction, the car will suddenly begin to drift towards the outside of the bend. If the rear wheels lose traction, the back of the car will begin to slew out sideways into a skid. If all four wheels hydroplane at once, the car will slide in a straight line, again towards the outside of the bend if in a turn. When any or all of the wheels regain traction, there may be a sudden jerk in whatever direction that wheel is pointed.
If the rear wheels hydroplane and cause oversteer, the driver should steer in the direction of the skid until the rear tires gain traction, and then rapidly steer in the other direction to straighten the car.
Electronic stability control systems cannot replace these defensive driving techniques and proper tire selection. They rely on the same braking mechanism at the driver's disposal, which in turn depends on road contact. While stability control may help recovery from a skid when the vehicle slows enough to regain traction, it cannot prevent hydroplaning.
Hydroplaning is a condition that can exist when an aircraft is landed on a runway surface contaminated with standing water, slush, and/or wet snow. Hydroplaning can have serious adverse effects on ground controllability and braking efficiency. The three basic types of hydroplaning are dynamic hydroplaning, reverted rubber hydroplaning, and viscous hydroplaning. Any one of the three can render an aircraft partially or totally uncontrollable anytime during the landing roll.
However this can be prevented by grooves on runways. This was initially developed by NASA for space shuttles landing in heavy rain. It has since been adopted by most major airports around the world. Thin grooves are cut in the concrete which allows for water to be dissipated and further reduces the potential to hydroplane.
Reverted rubber hydroplaning frequently follows an encounter with dynamic hydroplaning, during which time the pilot may have the brakes locked in an attempt to slow the aircraft. Eventually the aircraft slows enough to where the tires make contact with the runway surface and the aircraft begins to skid. The remedy for this type of hydroplane is for the pilot to release the brakes and allow the wheels to spin up and apply moderate braking. Reverted rubber hydroplaning is insidious in that the pilot may not know when it begins, and it can persist to very slow groundspeeds (20 knots or less).
When confronted with the possibility of hydroplaning, it is best to land on a grooved runway (if available). Touchdown speed should be as slow as possible consistent with safety. After the nosewheel is lowered to the runway, moderate braking should be applied. If deceleration is not detected and hydroplaning is suspected, the nose should be raised and aerodynamic drag utilized to decelerate to a point where the brakes do become effective.
Proper braking technique is essential. The brakes should be applied firmly until reaching a point just short of a skid. At the first sign of a skid, the pilot should release brake pressure and allow the wheels to spin up. Directional control should be maintained as far as possible with the rudder. Remember that in a crosswind, if hydroplaning should occur, the crosswind will cause the aircraft to simultaneously weathervane into the wind as well as slide downwind.