Hydroplaning and flooded roads

How hydroplaning starts

To grip a wet road, a tire has to push water out of the way. The grooves in the tread carry that water out to the sides and behind. When there is more water than the grooves can move, or the car is going too fast for them to keep up, water builds up in front of the tire and lifts it. For a moment the tire is riding on water, and the steering and brakes do very little.

Tire makers put the starting point as low as about 35 mph when there is enough standing water. Speed, water depth, tread depth and tire pressure all play a part, so there is no single speed that is safe in every storm. Slowing down is the one change that helps in every case.

Tread depth and water

Tread depth is the part you can measure. Tire retailers suggest replacing at about 4/32 of an inch if you drive in heavy rain, because a tire's grip on wet roads drops off as the grooves get shallow, well before it is worn out at 2/32.

The penny test finds tires at 2/32 or below. If your tires are close to that, a Houston downpour is the wrong time to find out how close.

When to replace your tires, and the penny test

Tire pressure in the rain

Tire makers list low pressure next to worn tread as a cause of hydroplaning. An underinflated tire does not hold its shape against the road as well, and the grooves do not clear water the way they were designed to.

Set the pressure cold, to the number on the driver's door placard, not the maximum printed on the sidewall. Check it monthly and before a long drive, the same routine NHTSA gives for every season.

How to check tire pressure in Houston heat

If the car starts to hydroplane

You may feel the steering go light. The advice from tire makers is the same across the board:

• Ease off the gas. Do not slam the brakes.
• Keep the steering wheel pointed where you want to go, with small movements only.
• Let the car slow down until the tires grip the road again.
• Skip cruise control on wet roads, so the car is not holding speed for you.

Once the tires grip again, slow down further. If it happened once on a stretch of road, it can happen again on the next low spot.

Before a stormy stretch

Storms in Houston rarely give much notice. A few minutes in the driveway beforehand covers the tire side of it.

• Run the penny test on all four tires, inside, center and outside grooves.
• Check the pressure cold and set it to the door placard.
• Check the spare, or find out whether your car has an inflator kit instead of one.
• Look for nails, cuts and bulges while you are down there.

If the tread is close to 4/32 and the forecast is wet, that is the time to look at tires, not after the first close call.

Flooded roads

Houston streets and underpasses can flood fast in a heavy storm. Water on a road hides what is under it: a pothole, debris, a washed-out edge. It also hides how deep it is.

We are not going to give you a depth that is safe to drive through. No single number holds for every car and every street.

What to check after driving through water

If you did drive through standing water, look the car over before you trust it on the highway. Most of the damage comes from what was hidden under the water.

Walk in and tell us what you drove through. We check the tires and wheels, the alignment and the brakes, and tell you what we find before any work starts.

Brake inspection, pads and rotors

Wheel alignment