Tires are probably not something you think about every day. But they’re an essential technology that touches countless aspects of our daily lives. Think about it. If you take a school bus, city bus, your mom’s car or even a bike to school, you wouldn’t get far without tires. The big trucks that bring food to your neighborhood grocery use them. And so do the forklifts that help pack those supply trucks. Delivery vans, mail carriers, ambulances, police cars – they all use tires.

Although there are solid rubber tires, the tires that you see on most typical transportation vehicles – cars, vans, buses and even landing gear for airplanes – are air-filled, or pneumatic tires. Pneumatic tires have been around for more than a century. In fact, R.W. Thomson applied for and received the first patent for a pneumatic tire in 1845. The style didn’t really catch on though. A little more than forty years passed before J. B. Dunlop received a patent for his pneumatic bicycle tire in 1888. Tire technology has come a long way since Dunlop’s original patent.

Tire Components Today
A pneumatic tire is made of an airtight inner core filled with pressurized air. A tread covers this inner core and provides the contact area with the road. The pressure of the air inside the tire is greater than atmospheric air pressure, so the tire remains inflated even with the weight of a vehicle resting on it. The tire’s air pressure provides resistance against forces that try to deform the tire, but it gives to a certain degree –providing a cushioning effect as the tire hits bumps in the road. Let’s take a closer look at the components and the assembly.

The bead is a loop of high-strength steel cable coated with rubber. It gives the tire the strength it needs to stay seated on the wheel rim and to handle the forces applied by tire mounting machines when the tires are installed on rims. The body is made up of several layers of different fabrics, called plies. The most common ply fabric is polyester cord. The plies are coated with rubber to help them bond with the other components and to seal in the air. A tire's strength is often described by the number of plies it has. Most car tires have two body plies. By comparison, large commercial jetliners often have tires with 30 or more plies.

In steel-belted radial tires, belts made from steel are used to reinforce the area under the tread. These belts provide puncture resistance and help the tire make good road contact. The sidewall provides lateral stability for the tire, protects the body plies and helps keep the air from escaping. It may contain additional components to help increase the lateral stability. The tread is made from a mixture of many different kinds of natural and synthetic rubbers. The tread and the sidewalls are extruded and cut to length. The tread is just smooth rubber at this point; it does not have the tread patterns that give the tire traction.

Sidewall Signs If you look at the tires on your family car, you'll see every tire is stamped with letters and numbers like P205/55R16 91H. Here's what it all means: the "P" stands for passenger. The number 205 is the actual width of the tire. The "R" means it's a radial tire. The "16" is the width of the rim the tire fits on. The "91" indicates the load capacity - this one can support 1356 lbs. And the "H" lets you know how fast you can safely go - this one can go up to 149 mph.

Assembling a Tire

Photo courtesy Goodyear A tire designed to help prevent hydroplaning

All of these components are assembled in the tire-building machine. At this point, the tire has all of its pieces, but it's not held together very tightly, and it doesn't have any markings or tread patterns. This is called a green tire. The next step is to run the tire into a curing machine, which functions something like a waffle iron, molding in all of the markings and traction patterns. The heat also bonds all of the tire's components together. This is called vulcanizing. After a few finishing and inspection procedures, the tire is finished.

Making Contact
The next time you get in a car, take a close look at the tires. You will notice that they are not really round. There’s a flat spot, called the contact patch, on the bottom where the tire meets the road. The contact patch and air pressure in a tire are important. In fact, many people recommend checking tire pressure monthly. The tire pressure should never exceed the maximum (over inflation) that’s listed on the side of the tire. Misalignment, over inflation and under inflation can cause improper wear. Improper wear can affect how tires handle – or grip – the road.

Water is something else that can affect how your tires grip the road. Hydroplaning can occur when the car drives through puddles of standing water. If the water cannot squirt out from under the tire quickly enough, the tire will lift off the ground and be supported by only the water. Because the affected tire will have almost no traction, cars can easily go out of control when hydroplaning.