Jasper County Democrat, Volume 19, Number 67, Rensselaer, Jasper County, 18 November 1916 — WHY YOUR TIRES BLOW OUT [ARTICLE]

WHY YOUR TIRES BLOW OUT

“Underinflation” Bends the Fabric and Generates Beat. Ask a tiremaker why tires break down and he will promptly answer “underinflation” or “overloading,” which is the same thing. A highly inflated tire is almost as hard as solid rubber. Let out some -of the air, and its springiness increases. Since most of us ride for the joy of it, we are inclined to pump air into our tires too sparingly. The car bowls along easily; the tire absorbs all the shocks. But all the time the underinflated tire fabric is bending and bending at the sides, thousands and thousands of times, until at last the heated interior walls weaken and a loud explosion breaks upon the air. That incessant bending and straightening of side walls to which a tire is subjected generates heat. Bend a piece of wire back and forth in your hand many times and it will become so hot that your fingers can not hold it. Heat, similarly generated, breaks the chemical union between the inner fabric and the outer, rubber and reduces a tire to separate layers. No longer” are the strains equally distributed. One layer is pulled this way, another that way—moreover, with unequal forces. Blisters, corrugations, bumps large and small, appear on the surface. Tires are popularly supposed to blow out because they have been heated by the sun. No tire manufacturer makes allowances for hot weather. It is true that heat expands, but the amount of expansion due to the sun alone is negligible. A certain degree of heat is geherjj|ted in running over the road. But even that does not increase the air pressure as much as motor car owners believe. If the temperature of the air is 32 degrees Fahrenheit (cold enough to freeze water), if the tire is blown up to a pressure of seventy-two pounds a square inch and if the rise in the tire’s temperature at the end of a run is thirtyfive degrees, the total pressure within the tube will be seventyeight pounds, an increase of only six pounds. But if the thermometer records ninety degrees, as it often does on a summer’s day, the rise in temperature at the end of an equivalent run will be only thirtythree degrees, and the total air pressure 77)4 pounds, an increase of only 5 % pounds. Paradoxical as it may seem, the increase in pressure due to the sun’s heat is not nearly so great as motor car users suppose. For a given distance, it, is actually less on a hot than on a cold day.—Waldemar Kaemffert in McClure’s Magazine.