Dangers of aquaplaning
When driving on a dry road in the summertime, the driver hardly has to shed a thought for the tyres. When a thunderstorm breaks or a persistent summer rain fills the grooves in the road, it is quite a different ballgame. The danger of aquaplaning can be felt in the steering: it is difficult to control the car, especially if the tyres are in poor condition or worn out. The best way to prevent aquaplaning is to use new tyres. Even new tyres do not completely eliminate the risk of aquaplaning, but it is possible to control the car as long as you adjust the driving speed to the conditions.
From the viewpoint of traffic safety, it is important to have tyres with the proper groove depth and properties to suit the weather conditions. When there is plenty of water on the road and the driving speed exceeds a certain limit, the tread pattern of the tyre no longer pushes aside the water from underneath the tyre. The feel between the tyre and the road will be lost, and so will the grip.
When there is less than four millimetres of tread in the tyres, the tyres’ wet grip and aquaplaning properties essentially deteriorate; the risk of aquaplaning, in particular, greatly increases. Furthermore, the breaking distance is longer and the car will skid easier.
In recent tests conducted by Tekniikan Maailma (5/2018), worn tyres started aquaplaning at speeds as low as 75 km/h. The best new tyre in the test only started aquaplaning at 88 km/h.
Lost contact area
When the driving speed increases and the tyres wear out, the contact area between the tyre and the road is dramatically reduced. The below figure shows the size of the contact area of a summer tyre with various groove depths when driving at different speeds on a road with a water thickness of three millimetres. The contact area of a vehicle with worn-out tyres (thread 1.6 mm) and at the speed of 125 km/h is only 6 per cent when compared to a stationary vehicle.