Tread smartly on wet roads

The tyre maker was responding to rainy episodes in Gauteng which led to a spate of crashes in the first month of the new year.

“A tyre needs a firm grip on the road surface to ensure proper control,” said Bridgestone promotions manager Jan Maritz. “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,” he added.

Loss of traction caused by water on the road is known as aquaplaning. At 120km/h on a road covered with a film of just 1mm of water, the front tyres of a small sedan each need to clear away six litres of water per second. 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 120km/h. This is equivalent to dispersing a bathtub of water every three seconds.

Tyres disperse water 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 surface of the water. This is aquaplaning, and as any driver who has experienced it can attest, it 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. Many vehicles which experience aquaplaning crash before control is regained, so it’s important to prevent aquaplaning by reducing speed on wet roads and adjusting position in your lane to avoid deep standing water if possible.

“A major contributor to aquaplaning is insufficient tread depth,” Maritz explained. “Even if you’ve reduced speed on a wet road, a tyre with only a couple of millimetres of tread depth remaining might not be able to clear away enough water to prevent aquaplaning,” he said. “The legal limit is 1.6mm remaining, but anything below three millimetres is really not enough to cope with a severe rainstorm, even at reduced speeds,” he added.

He advised motorists to visit a fitment centre to have their tread depths checked. he explained. “A five-minute check could be the difference between safe control and aquaplaning when you next encounter rainy weather,” Maritz concluded.