Photo Courtesy of the Los Alamos

Pneumatic Tires

A pneumatic, or air-filled, tire is made of an airtight inner core filled with pressurized air. A tread, usually reinforced with steel belting or other materials, 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 -a cushioning effect as the tire hits bumps in the road. If you’ve ever taken a ride in an old-fashioned carriage with wooden wheels, you know what a difference a pneumatic tire makes.

Pneumatic tires do have drawbacks, especially in high-performance or highly dangerous applications. The main problem, of course, is that a puncture of the tire results in total failure. A blowout at high speeds can lead to a dangerous car accident. Military planners are concerned with tires getting blown out by gunfire or explosion shrapnel. A vehicle crew’s worst nightmare is getting trapped in a fire zone because their tires are all flat. Obviously, an airless tire can't be disabled by a single puncture.

A flat pneumatic tire

Another problem with pneumatic tires involves variations in air pressure and tire performance. Lower tire pressure can create improved traction (and increased comfort), because the tires “flatten” slightly, placing more tread in contact with the road. However, the pressure inside the tire doesn’t just maintain “up and down” stiffness - it also maintains the lateral stiffness of the tire. Reduced air pressure allows the tire sidewalls to flex, which unfortunately results in poor handling. In an airless tire, tire stiffness in those two dimensions is independent.

Air pressure causes other problems, as well. Consumers are notoriously unreliable when it comes to setting their tire pressure properly, often resulting in unsafe situations. Pneumatic tires are also susceptible to changes in temperature, which can change the tire’s internal pressure.