New tires can disperse up to 30 liters of water a second at 80 km/h, but with only the minimum legal tread depth of 1.6 mm remaining, water displacement drops to just over 50 percent of that level. Measurements made by Continental have shown that with a residual tread depth of three millimeters, tires still retain just over 80 percent of their water displacement capability. To determine this, the tire manufacturer ran a variety of tests with different tires. The tests showed that as tread depth decreases, all models of tire lose the ability to disperse larger volumes of water. So when tires reach the three millimeter limit, drivers should be looking to fit new ones. To help determine the residual tread depth, tire manufacturers such as Continental or Uniroyal have fitted “wet indicators” between the tread grooves. Standing three millimeters high, these indicator ribs are located between the tread blocks. If the surrounding tread has worn to the level of the indicators, it is time to replace the tires in the interests of the safety of all road users. The wet indicators can be found aligned with the raindrop symbol on the sidewall of the tires.
With new and run-in tires, drivers always need to slow down in the wet to avoid the risk of aquaplaning. If aquaplaning should nevertheless happen, drivers should take their foot off the gas immediately and depress the clutch. Avoid moving the steering wheel or braking, although if an accident threatens, emergency braking should be initiated at once – in most cases the rear wheels still have enough grip to slow the vehicle. As soon as the tires are back in contact with the road, drive on at reduced speed.