What is the tire pressure of a commercial jet?

Commercial airplanes are large and complex machines with many critical components, but some of them are a bit more familiar to us ground-crawling creatures. Planes have tires and your car has tires. Do you know what tires commercial jets are using? How much do they cost? And what is the pressure in those large Boeing tires?

Airplane wheels are unique in that they are not directly powered by any engine. Airplane tires experience the most damage during the landing and they last approximately 300 cycles (takeoffs-landings). Manufacturers provide recommended replacement periods, but maintenance crews also have to pay attention to the visible signs of wear. Airplane tires can be retreaded – the entire outer surface with tread can be replaced.

Airplane tires have little in common with the ones your car wears. They do not need to perform that well in corners and the span of operating conditions is actually quite narrow. Although airplane tires have a distinct tread pattern, it is not as deep or sophisticated as that of an automobile tire. The purpose of the tread is to remove water from the contact surface and improve grip, especially when the airplane lands in crosswind conditions.

Airplane tires are made from a rubber compound that can withstand huge temperature changes. The temperature on the ground can reach 40 degrees Celsius, but at a cruising altitude of 9-11 km thermometers can show -50. Therefore, the rubber compound must be be able to deal with such temperatures well without cracking or losing its properties. and lose its properties too quickly. Because of this temperature difference, airplane tires are not inflated with air.

There is water in the air, which quickly freezes and turns into crystals. Air density also changes with temperature. That is why airplane tires are often filled with nitrogen, which is non-flammable (unlike oxygen in the air), contains almost no moisture, and is a lot more stable in terms of pressure.

Speaking of pressure, the 15 bar pressure maintained in Boeing 777 tires is a fairly standard figure. For comparison, most car tires are inflated to 2.5-2.7 bars. That pressure is frighteningly high. When airplane tires are tested, they are filled with water, because it, unlike air, does not store energy as a spring. It’s safer that way.

Bursting tires are a big deal in aviation, which is why all commercial airplane tires have thermal valves. They melt at a certain predetermined temperature and allow the tires to deflate, instead of exploding in a violent and dangerous outburst.

Boeing 777-300ER tires have a diameter of 134 cm and weigh about 120 kg. The B777 has as many as 12 wheels – the heavier the aircraft, the more wheels it has. Meanwhile the front wheels of the Boeing 737 are relatively small, because the nose of the plane has less weight and less load during landing.

The front rims on the Boeing 737 are just 15 inches in diameter, which provides us with a great opportunity to compare these tires to those of a car. A 205/75R15 car tire would hold about 2.4 bars of pressure, while a 27×7.75-15 airplane tire is inflated to 14 bars. A car tire will be able to withstand a weight of approximately 725 kg, a B737 tire – 4377 kg. And there are two of them under the nose of the Boeing 737.

Finally, the manufacturer predicts that the front tire of a Boeing 737 will withstand speeds of up to 362 km/h, which is achievable only for top level sports cars. By the way, airplane tires are produced by the same manufacturers we all know – Good Year, Michelin, Dunlop and Bridgestone occupy approximately 85% of the market.