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How Fast is Too Fast When Driving On A Wet Roadway: Hydroplaning August 9, 2013

Posted by southbendpolice in Uncategorized.

Hydroplaning on water when you are driving occurs when the tires of a vehicle begin allowing roadway water to push underneath the tire because of increased speed. Tires are designed to channel the water and allow the tread to stay in contact with the roadway. Going too fast does not allow the channeling to occur, and the vehicle begins to ride on a cushion of water. That makes for a dangerous lack of control. Did you ever go inner-tubing behind a boat on a lake? Once you reach the proper speed, no real control exists for the occupant of the tube.

Now there are a lot of factors that can effect the loss of control, but studies have shown that when water depth reaches 1/10th of an inch for 30+ feet, hydroplaning becomes possible. In a moderate rainstorm or wherever water pools, that depth is easily attainable.

Without a long discussion of tire and tread design, lets look at a simple rule of thumb and try to figure out a sensible speed for driving in rain or a really wet roadway.

This formula was developed in the 1960’s when researchers studied the hydroplaning speeds of aircraft tires. It works for passenger cars and trucks as well and the results are far less than the average driver would generally guess.

Here is the simple formula:

Nine times the square root of your TIRE PRESSURE equals the speed in mph at which your vehicle will attain hydroplane speed.

At or above this speed you will be sailing along virtually frictionless, as if you were on water skis.

Fast example: Your tire pressure: 36 psi

The square root of 36 = 6

9 times the square root (6) = 54 mph

That’s your hydroplane speed at that tire pressure.

Incidentally, vehicle weight has absolutely no effect on hydroplane speed.

Example two: Your tire pressure: 32 psi

Square root of 32 = 5.66

9 times 5.66 = 50.9 mph

Please drive safely, especially when the roadway is compromised by snow, ice, dirt, debris and of course, water.

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