What is a Tire Tread?

The tire tread refers to the rubber around the outer circumference of a tire, the area of the tire that makes contact with the road. The tire tread is the part of the tire that the tread grooves that gives the tire its traction. Passing your annual auto inspections can depend on the depth of the tire's tread.

Tire grooves play an essential role in every automotive safety inspection because they play an important role in your safety behind the wheel. One of the essential roles of the tire grooves is to prevent water build-up between the tire surface and the road. It's the lack of sufficient tire tread that causes cars to hydroplane on water covered roadways. Hydroplaning, also known as aquaplaning, occurs when the water build up between the tires and the roads surface turns your car into an uncontrollable sled. The ratio of tread to airspace directly affects the traction and control your tires provide.

The part of the tires tread in contact with the road is known as the tires "contact patch" refer to the part of the tire tread that is in actual contact with the road surface. The size of the contact patch varies directly with the weight of the vehicle and inversely with the tire inflation pressure. The greater the vehicle weight, the larger the contact patch. The higher the inflation pressure, the smaller the contact patch. These two affects are not directly proportional. A decrease 15 percent decrease in inflation pressure or a 15 percent increase in vehicle weight doesn't increase the size of the contact patch by 15 percent.

The depth of your tires tread, the depth of the grooves in your tires will determine whether they pass or fail the safety inspection. The Motor Vehicle Department in the United States make tire replacement mandatory when there's 2/32 inches (1.587 mm) of tread remaining. Modern tires manufactured in North America have a built in tread indicator to notify drivers when there's only 2/32 inches (1.587 mm) of tread remaining. North American tire manufacturers mold a tread wear indicator into the remaining 2/32 inches (1.587-mm) of tread called "wear Bars." When these bars make their presence known, you have to replace the tires because they are no longer safe to drive on. That's the law but the prudent driver doesn't wait until the law demands that he or she buys new tires. The prudent driver knows that they need new tires when the grooves in their tire tread wear down to 6/32 inches (4.762 mm). You should know that less than 4/32 inches (3.175 mm) of remaining tire tread makes your vehicle prone to aquaplaning and less than 6/32 inches (4.762 mm) of read makes them hazardous when driving in snow.

Tire tread depth gauges are relatively inexpensive and every driver should have one in the glove compartment of every vehicle that he or she owns. In a pinch, you can use a coin to get a rough estimate of tread depth. Place a penny in several of the tire grooves across the tire. If part of the Lincoln head is always covered, you have, at least 2/32 inches (1.587-mm) of viable tread depth left. Place a quarter in several of the grooves across the tires tread area, if part of Washington's head is always covered you have more than 4/32 inches (3.175 mm) of viable tire tread depth left. Place the flip side of the penny in the tire grooves, if the top of the Lincoln Memorial is always covered, there's more than 6/32 inches (4.762 mm) of viable tread depth remaining.