Tread smartly on wet roads

With Gauteng’s rainy season in full swing, the risk for vehicle crashes is high. In the first month of the year the province experienced a spate of crashes as a result of the wet weather. Tyre maker Bridgestone says inadequate tread depth could be a contributing factor because it can lead to aquaplaning.

Bridgestone promotions manager, Jan Maritz, says most drivers associate loss of traction with situations like skidding, which is frequently caused by abrupt steering or excessive speed when cornering. But loss of traction can also be caused when a tyre encounters more water than it can clear away. This is called aquaplaning.

“A major contributor to aquaplaning is insufficient tread depth,” Maritz explains. “Even if you’ve reduced speed on a wet road, a tyre with only a couple of millimetres of tread depth might not be able to clear away enough water to prevent aquaplaning,” he says. “The legal limit is 1,6 mm remaining, but anything below three millimetres is really not enough to cope with a severe rainstorm, even at reduced speeds,” he adds.

On a road covered with a film of just one millimetre of water, the front tyres of a typical small sedan each need to clear away six litres of water per second if the car is travelling at 120 km/h. During a heavy downpour, where standing water may be a centimetre deep, each tyre needs to clear away 60 litres of water per second at 120 km/h says Bridgestone.

According to the tyre maker, tyres clear water away by channelling it between the gaps and grooves in the tread and mopping up excess water with small slits in the tread blocks – called sipes. However, if the speed is too high or there is too much water on the road, the tyre’s ability to disperse water becomes overwhelmed and it lifts off the road surface to skim along the water. This aquaplaning can make it impossible to brake, steer or accelerate.

Aquaplaning only ceases when the water depth drops below the critical limit or the vehicle’s speed slows enough for the tyre to regain contact, but many vehicles crash before this.

Bridgestone encourages motorists to prevent aquaplaning by reducing their speed on wet roads and avoiding deep standing water if possible. It also emphasises the need for adequate tread depth to help motorists avoid aquaplaning.

Maritz advises motorists who are concerned about their tread depths to visit a fitment centre to have them checked. “Fitment centres have tread-depth gauges to check how much remaining tread your tyres have, and also to ensure that treadwear is even across the tyre surface,” he explains. “A quick five-minute check could be the difference between safe control and aquaplaning when you next encounter rainy weather,” he concludes.