One of the big hazards of summer rainstorms for drivers is hydroplaning, when your car loses contact with the ground, and instead floats uncontrollably on a layer of water. It seems impossible–a ton of vehicle being undone by less than a quarter-inch of water–but any heavy rain is guaranteed to bring hydroplaning wrecks.
According to a web page for the University of Pittsburgh Safety & Security Committee, hydroplaning happens when the water on the road in front of your tires accumulates faster than your tires can push it out of the way. (That’s one of the roles of tire tread: to provide a channel for the water to be pushed backward.) The water forces its way between the road and the tire, and raises the car via water pressure. Not a lot, just a tiny fraction of an inch… but that’s enough to make your car “float.”
The effect is like hitting a patch of ice–you lose control, including the ability to brake and steer.
There are three factors that contribute to the risk of hydroplaning during a storm:
- Depth of Tire Tread. Another good reason to check your tire tread–worn tires can’t channel water away, and are more likely to cause hydroplaning.
- Speed of Car. The faster you’re going, the greater the risk of hydroplaning. Slow down in a heavy downpour, even if you know the road.
- Depth of Water. The deeper the water, the more quickly you’ll lose traction. But you don’t have to have puddles to be at risk–even a strong rain can build up quickly.
According to the University of Pittsburgh, it can be difficult to tell if you are hydroplaning before that frightening moment when you realize you have no control:
“The rear end of your vehicle may feel a little squirrelly (loose, giving you the sensation that it has moved to one side or the other), especially in a high crosswind. The steering may also suddenly feel loose or little too easy. Watch the road ahead for standing or running water. You can also pay attention to the spray being kicked up by the cars in front. If it suddenly increases it’s possible that the driver has hit a patch of water that could cause you to hydroplane.” University of Pittsburgh engineering
WHAT TO DO
If you find yourself beginning to hydroplane, first, don’t panic…don’t apply brakes…don’t try to turn the steering wheel. These could throw you car into a skid. Instead:
- Hold the steering wheel firmly, and keep going straight.
- Ease your foot off the accelerator until you can feel the tires grip the road again, or until you come to a stop.
- If you must apply brakes (and if you have anti-lock brakes), brake with a slow, steady pressure. Do not “pump” the brakes. The anti-lock mechanism automatically mimics pumping better than your foot can do it.
It is always important to drive at speeds appropriate to road conditions, and in a downpour, water accumulation is one of those “invisible” conditions. Slow down in the rain…always.
For a really old, but still technically valid, video about how hydroplaning happens, click here to go to an archive page from NASA: Automobile Tire Hydroplaning