When you take a close look at tires on some race cars, it looks like they’re totally worn down with no tread left on it at all. But these “racing slicks” are manufactured that way, completely smooth for best performance.
So should we wear our car tires to complete baldness, or buy some with no tread to start with? Not at all. Racing slicks are for absolutely dry weather on a closed circuit with no rain, no water from neighbors washing their cars in the driveway, no squished tomatoes that fell off a farm truck, and no grass cuttings from a thoughtless resident who lets the mower blow it all into the roadway, endangering the lives of motorcyclists. All that slippery stuff will turn a bald tire into a hydroplaning device. Ground contact is lost easily, and without that friction from the ground, the vehicle goes out of control.
A layer of rainwater on the road is very slippery. It gets worse when the road has just been resurfaced, and oil is still bleeding out of the asphalt. In Georgia, we’re now approaching the season where rain comes at irregular intervals. Summer rain showers are localized but strong. That can mean many days of dry road surface, accumulating oil from vehicles. When the rain comes, it floats the oil to the top because water is heavier than oil. The result is immediate slickness. Police officers know that crashes are most frequent just a few minutes after the rain starts, before the oil film gets washed away.
To deal with this problem, tires need a deep, patterned tread. The grooves and their intersections channel rainwater from the roadway and force it away from the tires. A typical car tire touches an area (the “contact patch”) that’s about the size of a cereal bowl or coffee saucer. Once it reaches its wear limit, the grooves are getting so shallow that they can no longer displace water quickly, and the tire becomes unsafe. There’s an easy way to check. Run your finger through the nearest groove. At some spots, there’s a raised bump, the “wear indicator.” If it reaches the top of the tread, the tire is worn out and must be replaced.
Summer is coming, and we’ll be going through numerous fast and heavy rain showers. That’s where good tire tread saves lives.
Rudi Kiefer, Ph.D., is a professor at Brenau University, teaching physical and health sciences on Brenau’s Georgia campuses and in China. His column appears Sundays and at gainesvilletimes.com.