Rain is unfortunately a common occurrence during the summer - in fact, the Met Office gives an average of up to 300mm and over of rain during the UK summer season - which is more than enough to cause aquaplaning. Here we will discuss what aquaplaning is, how to safely drive through water and, perhaps most importantly, what type of summer tyres are best equipped to cope with it.
What is aquaplaning?
Aquaplaning, also known as hydroplaning, is a term used for when large amounts of water create a layer between the tyres and the water. This can be a problem when driving, as the water-layer prevents any direct grip or control on the road.
So, how can you tell if your vehicle is aquaplaning? A large majority of the feedback you get from your vehicle (in terms of the driver experience, handling and performance) relates to the contact area your tyres have with the road. The faster you drive, for instance, the smaller this contact area becomes - the same is also true for tyres that have worn down to a thinner tread. In these instances the car feels difficult to control, as if it is gliding on ice, because it cannot respond to your input correctly. Aquaplaning gives off the same feeling, as the water layer prevents direct contact with the harder road surface. Even the best car performance tyre can do very little if it’s not making direct contact with the road
Normally, when driving on a wet road, the weight of your vehicle is able to push enough water out of the way. It’s during aquaplaning, however, that the volume of water is too much for your wheels to move aside with force. Instead, it builds up underneath, causing pressure and pushing your vehicle up as a result.
So how much water on the road is needed for aquaplaning to be a risk? There is no one definitive answer as various factors, such as the type of car and the choice of tyres makes it hard to determine. However, at least one study suggests it takes just 2.54 mm (one-tenth of an inch) per 30 feet or more. You also have to consider the environment around you, such as whether or not there is anywhere for the water to run-off to (such as grassland or drainage systems).
What influences the grip on a wet surface?
Properties of a specific tyre model
The variety of tread patterns found today is huge. Some manufacturers prefer the asymmetric tread type, others directional, and others remain faithful to the symmetrical pattern. They all behave differently on wet surfaces.
Too low tyre pressure
A tyre that’s rolling on a wet road creates a wedge of water in front of it. The impact of the tread against the water in front of the contact surface creates hydrodynamic pressure. When this pressure exceeds the pressure inside the tyres, water can no longer be repelled and the tyre lifts off the road surface.
You can calculate the hydrodynamic pressure using this formula:
The diagram below shows the influence of correct tyre pressure on the size of the contact zone with the surface:
Tyre imprint shape
As mentioned earlier, a wedge of water forms in front of the rolling tyre on a wet road. It must be effectively dispersed sideways before the pressure it exerts on the leading edge of the contact surface exceeds the tyre pressure. It is commonly known that a flat shape has more resistance than a rounded shape. This is why watercrafts usually have a V-shaped or just rounded bow. Similarly with tyres: the more rounded the shape of the contact zone, the more water will dissipate, the lower the hydrodynamic pressure will be, and the higher the speed at which aquaplaning will occur.
The previously presented formula can be expanded to take into account the water dispersion angle resulting from the shape of the contact zone. This way you will calculate the value of the hydrodynamic pressure for a given surface.
This shows us that the greater the angle, the lower the hydrodynamic pressure will be.
Tyre width
The probability of aquaplaning is bigger, the greater:
- the tread pattern is worn and the tread pattern density is greater (i.e. the proportion of tread grooves is small)
- the travel speed
- the water layer on the road
- however, the air pressure in the tyre must be lower.
All these elements are related to the amount of water that must be repelled through the tread. It can be calculated on the basis of the following aquaplaning formula:
Using the formula above you can calculate how many liters of water must be repelled from under the tyre during each second of movement.
How to manage aquaplaning
If you experience aquaplaning, it is important that you remain calm - most instances of aquaplaning happen for only a few seconds at best, but the wrong response can make things worse.
Whatever you do, do not try to accelerate or brake. Since the tyre’s are not connected to the ground, because of the inbetween layer of water, this won’t have the effect you expect.
Braking will not be effective, as the tyres won’t be able to break against the road, and the same goes for accelerating, for the same reason. In fact, at increased speeds you’re more likely to encounter aquaplaning, as a higher speed causes the tyre to glide across the water, rather than forcing the water away.
What you should do is release the accelerator, so you can allow your vehicle to slow down naturally. This will give you some control back, as the tyres begin to ‘sink’ and touch the ground. It should only take a moment for the tyres to make contact with the surface, allowing you to gain complete control again.
Choosing the best performance tyres for aquaplaning
Some of the leading summer tyres offer grip on wet surfaces as a major feature. In fact, it’s one of the main categories included in EU tyre labels, so you can easily find a tyre that offers better performance during aquaplaning and similar conditions.
As we’ve mentioned before, the best performance tyres for aquaplaning need to have the right treads or tread pattern. A good tread depth is also needed - at least 3 to 4 mm - as this enables the grooves to actually divert or expel water away from the vehicle.
It is also recommended that you choose a directional or asymmetric tread pattern. For the former, the directional design offers liquid expulsion, creating an unparalleled resistance to aquaplaning. By pushing the water out, it won’t build up between the tyre and road surface. For the latter, asymmetric tyres have smaller blocks on the inside, which offer a better grip on wet surfaces and are suited for cars with bigger engines and more power.
The tread depth is also important, since the deeper your tyres are, the more tread design there is to provide expulsion. Older tyres will often be worn down, as the tread is one of the first parts to be affected by wear and tear.
For the most part, aquaplaning is not a problem commonly encountered. It is only when enough water builds up that it may occur. Yet, due to the high volumes of rain, it is always better to be prepared with the right car tyres.