Aquaplaning

The following social media message is again being shared across the world, many years after it first appeared.  As with all things on the web, I am always distrustful of things like this, but it did get me to thinking about whether there was any truth in it!

  “A 36-year-old female was travelling between Wollongong and Sydney. It was raining, though not excessively, when her car suddenly began to hydroplane and literally flew through the air. When she explained to the policeman what had happened, he told her something that every driver should know – NEVER DRIVE IN THE RAIN WITH YOUR CRUISE CONTROL ON. The policeman told her that if the cruise control is on and your car begins to hydroplane – when your tyres lose contact with the pavement, your car will accelerate to a higher rate of speed and you take off like an airplane. She told the policeman that was exactly what had occurred. The policeman estimated her car was actually travelling through the air at 10 to 15km/h faster than the speed set on the cruise control. The policeman said this warning should be listed, on the driver’s seat sun-visor – NEVER USE THE CRUISE CONTROL WHEN THE PAVEMENT IS WET OR ICY.”

 Although the story is a total myth, the actual advice is right!  This is why ….

Aquaplaning (Hydroplaning)

Those of you that have attended our classroom session will know that aquaplaning is the total loss of grip due to the build up of water between the road and your tyre.  Wikiepedia sum it up very nicely with “If it occurs to all wheels simultaneously, the vehicle becomes, in effect, an uncontrolled sled. “

It is caused by a tyre tread not being able to dissipate the water on the road, with the water building up a wedge in front of the tyre, which then lifts the tyre making it lose contact with the road.  When contact with the road is lost, so is any grip, causing the tyre to skate across the water.

aquaplaning-all

Pre-requisites

There are a number of pre-requisites required before a tyre will aquaplane.

Tyre tread is the most obvious one.  The less depth of tread on a tyre, the less water the tyre will be able to disperse.  A half worn tyre will aquaplane at approx. 3-5 mph lower speed than a full tread tyre.

Tyre pressure, if tyres are under inflated, the only part of the tread that will be in contact with the road is the edges of the tyre only.  This means all the tread across the middle of the tyre will not disperse the water.

Unbalanced tyres causes uneven tread wear, which then means the tread is not as efficient at dispersing the water.

Water.  There needs to be a large enough area of water of a sufficient depth that the tyre cannot disperse the water, and that will build up a wedge of water in front of the tyre.

Speed of vehicle is key.  In it’s report ’Don’t lose your grip in wet weather’, *Consumer Reports tested various tyres at numerous speeds through water of 3/8th inch.  They found the good tyres began to aquaplane at speeds over 50mph, however some of the poorer tyres began at 47mph.

Light rain after a long dry spell can mix with the oil residue on the road to create a very slippery surface that can cause a vehicle to exhibit the same lack of handling and control as aquaplaning—but at much lower speeds in the 35mph range.

 How to avoid aquaplaning

These will mainly be obvious, as most are based on the causes above!

► Keep your tyres at the correct tyre pressure

► Always ensure you have a good tread depth.  A new tyre stars of with 8-9mm of tread, and the legal minimum is 1.6mm across 75% of the centre of the tyre.  However, it is recommended that you change your tyres well before the 1.6mm mark, preferably at about 3mm.

► Take care when driving in the outside lanes of dual carriageway/motorways as this is often where water tends to accumulate

► Follow the tracks made through water by the vehicle in front – his tyres will have already dispersed some of the standing water

► Slow down when there may be standing water, the higher the speed the less water dispersed

► If you need to change speed or direction, do it carefully and smoothly

► Do not use cruise control, as this will take away some of your control of the car (see below)

How to recognise aquaplaning

Basically, if you drive through standing water and your car suddenly feels vey light and possibly starts to change direction, and you feel as though you are driving on ice.

Aquaplaning can affect all four wheels or a combination of wheels:

► If your drive wheels aquaplane, your engine RPM and speedometer are likely to increase as the wheels spin trying to get traction

► If your front wheels aquaplane, your vehicle will slide towards the edge of the road, especially if you are in a rear-wheel drive vehicle as the rear wheels will keep pushing you forward

► If your back wheels aquaplane, your cars rear end will start to skid.

► If all your four wheels aquaplane, your vehicle should carry on in a straight line, and again your speedometer/engine revs will increase

When the tyres regain traction, there is likely to be a sudden jerk, and a change in direction if you have moved the steering wheel.

What to do if you aquaplane

In the vast majority of cases, the best course of action is to do nothing.  Aquaplaning will normally only last less than a second, so the best thing to do is be prepared for when the tyres regain traction.

If you were travelling in a straight line, gently easing back on the accelerator may reduce your speed enough for the tyres to regain traction.  Never ever stamp on the brakes.

If your rear wheels only aquaplane and you feel the rear end skidding, control the car as you would normally for a rear wheel skid, i.e. if the rear is sliding out towards the edge of the bend, gently steer in the opposite direction until the point where you feel the rear wheels gripping (e.g. an oversteer skid).

Okay, so back to the original Cruise Control question!

In the social media story, the car ‘began to hydroplane and literally flew through the air’.  There is absolutely no truth that aquaplaning with or without cruise control will cause a vehicle to fly through the air, nor gain speed of up to 15 km/h.

Cruise control may cause a vehicle to slightly increase speed if aquaplaning, as in some cars the cruise control does not recognise the aquaplaning as a loss of traction, but as deceleration, and applies power.   As previously said, aquaplaning is likely to last less than a second, therefore the speed increase will not be great.

The most likely scenarios of perceived issues with cruise control and aquaplaning are:

► When using cruise control the driver no longer has the feel of the road through the accelerator.  Therefore they will not get the initial heads up via the accelerator and only feel the car start to aquaplane when the steering becomes very light.

► Cruise control is usually taken off by touching the brake, and it could be the driver hits the brake too hard in their panic when trying to disengage the cruise control.  This could cause the wheels to lock up, resulting in no loss of speed.  ABS will alleviate this to some extent, however stabbing the brake is not a good idea.

► When people use cruise control, they often move their feet away from the pedals, which, once the car starts aquaplaning, would cause a delay while the driver moves their feet back to the pedals, resulting in a critical delay before they take control back

► As the cruise control is on, the driver cannot gently lose speed using accelerator sense, and has to use the brake.

► There is also a suggestion that when a driver panics and tyres to stab the brake they hit the accelerator by mistake, and this could also cause a speed increase once tyres regain traction

► If a driver is negotiating a bend in a rear-drive vehicle, the cruise control would not identify a lack of traction with the front wheels, and would, therefore keep applying the power which would push the vehicle forward in a straight line (rather than round the bend)

► Finally, using cruise control can make a driver inattentive, and the time it takes the driver to realise there is a problem it is too late.

Therefore, whilst the original story is an urban myth, the advice is very good – Do Not use cruise control in poor weather conditions such as ice, snow and rain, where greater control is required.

 

 

 

 

 

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