When General Motors responded to the Federal Motor Vehicle Safety Standards Act in 1967, I was assigned to survey the Quality systems of tire and wheel manufacturers supplying General Motors. There were five wheel manufacturers and twenty eight tire manufacturers in the United States supplying those components to GM at that time. I surveyed each plant four times per year. I learned a lot about tires and what affects their performance. During my tenure on this job, the manufacturers moved from bias ply tires to bias belted tires and then to radial tires. I visited GoodYear in Akron, Ohio many times and was exposed to a lot of tire engineering and testing as well as manufacturing and quality control.
Testing was very enlightening. I witnessed airplane tire testing that simulated aircraft landing and departure. The testing apparatus was a large ‘bull wheel’, perhaps 6 feet in diameter and a foot wide that represented the landing surface. The tire being tested was mounted on a device much like a landing gear on an airplane positioned above the bull wheel.
The test began with the bull wheel rotating at a surface speed simulating landing speed of an airplane (about 160 mph). The landing is simulated as if it was an airplane landing. The test tire is slammed into the bull wheel with the same force of a landing airplane just as you see when an airplane lands. Smoke flies and the tire squeals as it comes to speed and as the brakes are applied bringing the bull wheel to taxi speed. The airplane load is applied and maintained as this is happening. Then the bull wheel rotates slowly simulating the taxi to the terminal with the load of the aircraft maintained. After a static rest period simulating passenger movement, aircraft load and unload of baggage, freight and fuel, etc. then the taxi back to the departure point is simulated. Aircraft departure and “take-off” are simulated and the process stops, simulating flight. This process is run repeatedly until the tire fails. Interestingly, my escort told me that the tire always fails during simulated departure or ‘take-off’. I questioned this statement and my escort said, “Always”, because that is when the tire is at maximum load and maximum temperature, having just experience the landing, taxiing and take-off and because the tire is likely loaded to or near it’s capacity.
Real Life Tire Failure
The testing scenario above supports the fact that a major contributor to tire failure is heat. As the temperature of a tire rises, the tire becomes heat ‘soaked’ through and through, contributing to separation of the cord body and a breakdown in the rubber. Heat is generated in a tire by under inflation and overloading and of course friction. Under inflation causes excessive sidewall flexing which heats up the tire. Overloading has the same effect. Excessive friction from side slipping and spinning on the road surface also adds heat contributing to shorter tire life. Excessively worn tires with less tread depth also contributes to tire failure. Tread depth contributes to cooling, thus tires with little or no tread can overheat. You may observe that some race car tires have no tread, except when racing in the rain. Race tires are used in very controlled conditions and only last a few hundred miles.
So, inspect your tires often, keep them properly inflated and do not overload the vehicle for safe motoring.