It had stopped raining when Jim Sweeney, of Happy Valley, Ore., was driving his 2001 Toyota Highlander at about 60 mph on an Oregon interstate. Suddenly, he saw shallow water covering the road ahead. As the SUV hit it, Sweeney felt the car "float," as if it had lost contact with the road. The rear end drifted slowly to the left, causing the wheel to hit a barrier. The Highlander spun 180 degrees and slid backward and sideways across the highway, off the road, and, luckily, into a parking area, where it finally came to a stop.
The problem was hydroplaning. And many victims aren't as fortunate as Sweeney. Hydroplaning happens when water causes a vehicle's tires to lift off the road surface. That makes you lose control of the car; you can't steer or stop.
Many people assume that water has to be deep to cause hydroplaning, but even a thin film of water can cause problems, especially if you're driving too fast or your tires are worn. Hydroplaning happens quickly and, unfortunately, there's not a lot you can do except lift off the gas pedal and coast until steering feel returns. But there are ways that you can avoid trouble.
The faster you drive, the greater the risk of hydroplaning. The photos at right show how a vehicle's speed affects the degree to which a tire's tread separates from the road when you're driving through standing water. If water is sheeting across the road or pooling in areas, take extra care and cut your speed far below the posted limit.
The grooves in a tire's tread are designed to resist hydroplaning by allowing water to flow through them and out from the space between the tire and the road surface. But some tires do that better than others.
To evaluate a tire's resistance to hydroplaning, we drive a car at successively higher speeds through a section of our test track that's covered in 3/8 inch of water until its tires lose touch with the pavement. In our last test of regular all-season tires, some started to hydroplane at speeds as low as 47 mph; the better ones resisted hydroplaning until the car reached 55 mph. The Michelin HydroEdge and the Continental ProContact EcoPlus+ are recommended tires that provide very good hydroplaning resistance.
Keeping your tires properly inflated also helps. Check them at least once a month.
As a tire wears, its tread grooves become shallower, which reduces the amount of water that can be channeled through them. That diminishes the tire's capacity to prevent hydroplaning. When we tested all-season tires with the tread shaved to simulate being half worn, we found that hydroplaning set in at a speed about 3 to 4 mph lower than it did with full-tread tires.
That's one reason we recommend shopping for new tires well before the tread depth reaches 1/16, the legal limit in most states. You can easily check tread depth by inserting a quarter into a tire's deepest grooves, head pointing down. If you can see the top of George Washington's head, you have 1/8 of tread or less, and it's time to start shopping for new rubber.
Give standing water the same respect you would give ice. If you can, drive around large puddles. And try to stay away from road edges, where water collects.