What is aquaplaning and how to avoid it

Find out all you need to know about aquaplaning and how to avoid it.

Losing control of your car is a frightening experience. If you have ever felt your car slide along a waterlogged stretch of road, then you have most likely experienced aquaplaning. Knowing what to do when this happens can help you avoid an accident.

Aquaplaning meaning

Aquaplaning, sometimes known as ‘hydroplaning’, occurs when the road is wet and a layer of water is created between the road and a car’s tyres causing a loss of traction as the car’s tyres are in contact with the water, not the road; until you reestablish contact between tyres and road, the car will be unable to steer, brake or accelerate and can become out of control.

Car tyres have grooves in the tread around their circumference whose role is to eject water to help maintain contact between the tyre and the road. If there is too much water for these grooves to work quickly enough, a film of water builds up and occupies the whole of the tyre’s ‘contact patch’ meaning the tyre is not in contact with the road service. This can be dangerous.

When does aquaplaning happen?

Aquaplaning usually only happens when there is a lot of surface water on the road, either because of heavy rainfall, and/or poor drainage. If the tyres encounter too much water too quickly, the grooves in their tread will be overwhelmed and unable to expel enough water, meaning the tyre is not in contact with the road.

The following factors can impact a vehicle’s likelihood of aquaplaning:

• Tyre width, pressure, and tread depth
• Speed of the vehicle
• Vehicle weight

New tyres have approximately 8mm of tread depth, this helps them dissipate water on the road while maintaining adequate traction. The minimum legal tread depth limit in the UK is 1.6mm. In wet weather, the difference in stopping distance from 50mph between a new tyre and one with the minimum legal tread depth can be up to 13 metres. When there is 2.5mm of standing water it can be much longer. That’s why changing your tyres when they have reached 3mm tread depth is a good rule to follow. Wider tyres have more water to displace and are more susceptible to aquaplaning.

The faster you go the more water each tyre must displace, so it’s always a good idea to slow down in adverse wet weather conditions, especially when you see standing pools of water on the road. Aquaplaning generally happens at speeds above 40mph.

Heavier vehicles will put more pressure on each tyre which can help them displace water more easily. However, a heavier car with very wide tyres can be just as susceptible to aquaplaning as a lighter car with narrow tyres. This is because the additional weight is spread out over a larger contact patch. So, you should never assume that you will be less liable to aquaplane just because you drive a heavy seven-seater SUV.

How do I know if I’m aquaplaning?

You may not realise your car is aquaplaning if it hasn’t happened to you before. These are the signs to look out for:

• Steering wheel feels lighter to turn than usual
• The car may swerve or drift from side to side
• The car won’t respond to steering inputs
• The revs flare up causing the driven wheels to spin
• The brakes don’t respond as expected

What to do when aquaplaning

The most important thing to remember if you begin aquaplaning is to try to remain calm. The second most important thing is to avoid jerky or sudden inputs to the steering wheel or brakes as when the car regains traction, you may make the situation worse if you are sawing away at the steering wheel and slamming on the brakes.

These are some of the things you should do when aquaplaning:

• Gently ease off the accelerator (to slowly decrease speed)
• Turn off the cruise control (if applicable, so the vehicle is fully in your control)
• Keep the car pointing straight (because when you regain traction, if the wheels are turned at an angle, you may veer off the road)
• Don’t slam on the brakes (gradually apply them once the car has regained grip. If you break heavily you may lose control of the car)

How can I avoid aquaplaning?

Driving well within your limits and with due regard to road conditions is always a smart idea, doubly so in slippery and wet conditions. Reduce your speed even further when approaching puddles or flowing water across the road.

It is much safer to go slower. Going faster increases the risk of losing control of the car if aquaplaning happens, and is likely to make any accident situation worse.

Your car should always be in roadworthy condition, with plenty of tread on the tyres, effective windscreen wipers and correctly aligned and clean headlights (which should always be turned on in conditions with poor visibility).

In summary:

• Keep your tyre tread depth above the 1.6mm legal minimum (Most manufacturers recommend changing them once they reach 3mm)
• Avoid driving through deep puddles and fast flowing water
• Ensure that your windscreen wipers work properly
• Avoid sudden steering wheel movements or heavy braking
• Check that your headlights are correctly aligned – and use your lights to maximise your visibility to other road users
• Slow down. The speed limits posted on most roads assumes you are driving in perfect weather conditions (not wet or slippery conditions)

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