Tyres on public roads are legally required to have a tread pattern. The primary job of the tread pattern is to expel water, which can affect the contact patch with the road in wet conditions, and to provide grip and traction.
When driving on wet roads at high speed, a wedge of water can build up between the tyre and the road surface. The tyre loses road contact, and the vehicle is no longer responsive to steering. This phenomenon is known as aquaplaning or hydroplaning.
If tyres cannot grip the road properly during aquaplaning, this lack of traction has enormous consequences for car safety. The driver effectively loses control of the vehicle and is unable to brake, steer or accelerate.
Aquaplaning or hydroplaning is most likely to occur when there is a build-up of heavy rainfall on the surface of the road. It can also happen when the tarmac of the road is so uneven as to cause large puddles of standing water to collect.
There are several ways to reduce the chances of an aquaplaning accident with your car:
Important to note is that sufficient tread depth is vital not just in extreme situations. Even at low speeds, there is a higher risk of having an accident or collision if the tyres are worn down.
New tyres are capable of dispersing up to 30 litres of water a second at 80 kilometres per hour. But the depth of the tyre tread wears down over the course of regular usage. Consequently, tyres disperse significantly less water as the depth of the tyre tread decreases.
If car tyres have only a tread depth of 1.6mm for example, then water displacement is effectively and dramatically reduced.
If tyres have a tread depth of 3mm remaining, tyres can still retain a high amount of their water displacement capability. After this point, the risk of hydroplaning increases dramatically. In addition, a diminished tread also affects braking performance. The more worn the tread on a car’s tyres becomes, the longer it takes to come to a complete stop, as test results show.
In a test performed at our test location called Contidrom, the braking distance was increased by 6.9 meters on tyres with the legal minimum tread depth of 1.6mm, compared to the full thread depth of 8mm. Tyres with a 3mm tread only took 2.7 meters longer to come to a full stop. On this basis, we strongly recommend that when tyres reach the 3mm limit, you should consider fitting new ones to the wheels.
Tyres have tread across their entire circumference. Tread depth measurements must be taken (for example using a depth gauge) in the main grooves that feature Tread Wear Indicators (TWI) on modern tyres.
In most European countries, the legal minimum tread depth for car safety is 1.6mm; that's when tyres are due for replacement.
To ensure that tyres offer the best possible performance, consider replacing summer tyres when they reach a depth of 3mm, and winter tyres when they reach a depth of 4mm. Furthermore, fit all four wheel positions with tyres of the same tread pattern design. And at a minimum, each axle should have a pair of tyres with the same tread depth.
To better help determine the remaining tread depth, we have fitted “wet indicators” between the grooves of the tyre tread. These indicator ribs stand 3mm high, located between the tyre tread blocks.
If the surrounding tread has worn down to the level of the indicators, then it's time to fit the wheels with new tyres as a preventative safety measure.
Whether your tyres are new or old, drivers should always slow down on wet road surfaces to reduce the risk of aquaplaning.
If aquaplaning should occur – which is still possible depending on weather and road conditions that a driver cannot prevent – drivers are advised to immediately take their foot off the accelerator pedal and depress the clutch. Avoid moving the steering wheel or braking suddenly.
However, if there is a danger of a collision or severe accident, the emergency brake should be initiated at once. In most cases, the rear wheels will still have enough grip to slow the vehicle.
As soon as the tyres are back in contact with the road and traction is regained, it should be safe to continue driving at reduced speed.