Aquaplaning or skimming over water on tyres was discovered by Scientists at the National Aeronautics and Space Administration's Reseach Centre at Hampton, Virginia, USA, where NASA had been examining plane landing and ground- handling problems. NASA's research was triggered specifically by the near crash of a Boeing 707 departing a slush covered runway at New York's John F. Kennedy (then Idewild) Airport in 1959. The aircraft had reached critical speed, just shy of rotation and takeoff, and refused to go any faster. The pilot finally yanked it free and the ship staggered into the air- barely.
It's now known from that research, that a car may be driven for miles on the verge of a skid without the driver knowing it. A puff of wind, or a gust from a truck, may send the vehicle spinning.
On wet roads, a vehicle becomes a 'boat'. Most people think vehicles slip on wet roads because water is 'slippery'. But NASA engineers, studying the plane skids learned that this is only part of the problem.
A NASA engineer by the name Harrin Eziaslav had discovered that a tyre revolving at high speed on a continuously moving test belt would stop turning when water was introduced between the tyre and the belt. This, it turned out, is characteristic of tyre aquaplaning, the apparent result of drag induced by the displacement of the water, a force sufficient to hold back a 707 trying to take off.
This may explain some of the mysterious accidents that happen 'for no apparent reason' (and are thus thrown into the 'speed related' basket) on rainy days.
In full scale experiments, NASA found that at less than 50kph with tyre pressure at 25psi the front tyres begin to lose contact with the road. At around 80kph they're lifted up on a tough film of water and only the outer ribs are touching (remember: vehicle control depends on the tyre 'footprint' on the road).
At about 90kph the front tyres lose all contact (after reading the information below which will give an idea of the real life speeds required, think of that next time you are driving in a downpour).
With good tyres, aquaplaning may begin when the wheels can be heard splashing in as little as 5mm of water. WARNING CLUES: Clear reflections of other cars and objects and/or appearance of raindrop 'dimples' in the water on the road surface.
What can be done? The best thing to do in heavy rain is follow the example of most other drivers and slow down. It is also a good idea to stop and adjust the air pressure.
If you will be driving long distances at sustained highway speeds it is advisable to put more air in the tyres- alot more air. Tests show that high pressure tyres can cut better into rain film.
Most new tyres have deep tread grooves through which water pressure can escape. Most new treads are about 8.7mm deep. If the midtread are worn 75% or about 2.4mm, replace with new tyres. There is almost zero traction with 1.5mm deep tread.
Drive in the 'tyre wipes' left by the cars and trucks ahead. On busy highways, at 80-90kph these usually leave a fairly wide track where little water remains. There is NO need to tailgate as even in heavy rain these wipes remain for several hundred feet.
The most common type of aquaplaning is called 'dynamic aquaplaning'. A stagnation pressure of water builds up ahead of a tyre. As car speed goes up, the tyre literally mounts this cushion of water. It rides on the water like a water ski. The water chokes the open spaces in the tread. For all practical purposes, the tyre is bald.
If it is your tyre, you have no more control of your car than if you were driving along on ice. A gust of wind can throw you into an uncontrollable skid.
Some authorities believe that a dynamic hydroplaning accounts for the majority of single car accidents in wet weather - for what this is worth if anything. (There is no research that I am aware of to support this estimate but their guess might be right.) As a rule-of thumb, tyre aquaplane speed in miles per hour is determined by multiplying the square root of the tyre pressure by 10.3. For example, a common tyre pressure is 32psi. The square root of 32 is about 5.7. Five point seven times 10.3 equals 58.7mph (94kph). Therefore 94kph is the danger point.
The other kind of aquaplaning is known as 'viscous aquaplaning'. it occurs on mirror smooth road, with badly worn tyres. Langley experiments, show that viscous aquaplaning can occur at speeds much lower than those required for dynamic aquaplaning and with a film of water only 1mm thick.
The water has a tough surface tension than even the hundreds of pounds of pressure from a smooth tyre can't break. This tension is the same thing that causes water to encapsulate itself into a dew drop.
Viscous aquaplaning is perhaps more treacherous than dynamic aquaplaning because one is less aware of the danger.
Car weight has nothing to do with safety from skidding. That's because the heavier the car, the bigger the footprint. Car weight per square inch of road remains essentially the same.
Unlike dynamic aquaplaning, raising the tyre pressure has almost no effect on viscous aquaplaning.
Here's another nutty factor in wet road driving: The highly inflated tyre is more dangerous at low speeds in a downpour because it supplies less traction, less rubber in contact with the road. So if the tyres have been over-inflated, to increase the maximum hydroplaning speed in anticipation of driving long distances on wet roads, be sure to deflate the tyre to normal pressures when driving at lower sustained speeds if you can safely pull over and do so.
1. Stay well below the estimated hydroplaning speed;
2. Keep tyres properly inflated;
3. Don't drive on badly worn tyres. Any tyre with a tread depth of 2.4 mm or less should be discarded.
Another factor in the scary phenomenon of aquaplaning is the size of the tyre footprint. The larger the footprint, the more efficiently the tyre will aquaplane. Since there is more tyre surface to mount the cushion of water, it becomes more difficult for the tyre to 'cut through' the water to get to the road to maintain friction.
The two factors of hydroplaning determined by NASA research, tyre pressure and footprint area, tended to support highway engineers' observations that the incidence of wet road skidding auto accidents had increased markedly since the introduction of low pressure, low profile, wide oval tyres in the interests of motoring comfort. "Tyres used to carry as much as 40psi and this...kept most cars out of aquaplaning range," says Blair Geddes,one of California's district traffic engineers.
With the inception of lower tyre pressures, the aquaplaning phenomena is a looming danger. As demonstrated above, a common tyre pressure is 32psi. The square root of 32 is about 5.7. Five point seven times 10.3 equals 58.7 (94kph). So travelling at the maximum speed limit puts a driver near the critical hydroplaning speed.
This is significant for drivers brainwashed by government propaganda who think that driving at our current limits makes them immune to danger. If they stick to the speed limit instead of observing the driving environment when choosing a speed they risk aquaplaning.
1. Determine the aquaplaning speed of your car's tyres by multiplying square root of the tyre pressure by 10.3 then converting from miles per hour to kilometres per hour. Stay below this speed on wet roads, especially if the tyre tread is well worn.
2. If practicable, increase your margin of safety when travelling in wet weather at highway speeds by increasing tyre pressure by 10 psi above the recommended pressure. Be sure to lower the pressure at the conclusion of the highway driving if it is safe to stop and do so.
3. Remember that a bald tyre can aquaplane in as little as 1 mm of water, a depth bound to occur on many highways during normal rainfall.
Remember too, that once a tyre aquaplanes, even when the car is travelling in a straight line, all control can be lost. A cross wind of no more than 16kph or a gust of a passing truck can send a hydroplaning car into an unrecoverable spin.
4. Drive in the tyre wipes of the vehicle ahead WITHOUT tailgating.
5. Equip your car with tyres whose tread have been ribbed circumferentially, rather than patterned and which have been 'siped' (tiny transverse cuts in the rib).
6. Next time your vehicle skids, remember: your best friends are four rolling tyres.