Popular Science Monthly 



To the right: A casing that is 

 badly rim-cut or broken just 

 above the bead. The flap be- 

 came misplaced because the tire 

 was improperly applied 



Below: A tire worn off by ruts. 

 The same condition results if a 

 tire is run on muddy roads that 

 have a frozen crust through which 

 it sinks, or against the curb 



109 



tire cannot bend 

 without heat- 

 ing the interior. 

 After a time 

 the rubber ce- 

 ment that 

 holds the in- 

 ternal struc- 

 ture together, 

 hardens ; the 

 layers no long- 

 er adhere to- 

 gether; a loud 

 explosion breaks 

 upon the air; it 

 is time to buy a 

 new tire. 



DonH Be Afraid of 

 the Stm 



Although tires are thus sensitive 

 to heat, it must not be supposed that 

 they are very much affected by the sun on 

 a hot summer day. It is true that heat 

 expands the air within a tire, and that the 

 resultant expansion manifests itself in in- 

 creased air pressure. But no tire manu- 

 facturer makes allowances for the heat of 

 the sun, simply because it is negligible in 

 the life of a tire. At the end of a day's 

 run, with the thermometer over ninety 

 degrees in the shade, the pressure within a 

 tire will never increase six pounds. 



Beware of a Little Cut 



Everyone knows that sharp stones, nails 

 and glass may cut through the tread and 

 cause a puncture. But other causes of 

 punctures are not so self-evident. The lug 

 of a screw-bolt, a tire-removing lever, the 

 inner head edges of the casing, sand, and 

 ther hard substances which have worked 

 their way into the casing are equally fruit- 

 ful causes of punctures. 



Out-and-out punctures, however, occur 

 rarely. A tread one-half an inch thick, 

 very tough, backed up by ply after ply of 

 the finest and strongest Sea Island cotton 



or the stoutest 

 cord, is not 

 easily pierced. 

 It is the little 

 cut, so insig- 

 i nificant ap- 

 ] parently, that 

 is more in- 

 sidious, be- 

 cause it is a 

 less obvious 

 danger. No 

 cut is so small 

 but mud, gravel 

 and dust can be 

 forced into it, and 

 that dirt bores its 

 way into the tread as 

 the wheel turns over hun- 

 dreds and hundreds of times. 

 Soon the original cut lengthens and 

 widens. More dirt enters. Finally, the 

 tread is completely pierced, and the dirt 

 begins to wedge the tread away from 

 the inner fabric. Often "boils" appear 

 as the visible evidence of the process of 

 destruction. Then comes the inevitable 

 blowout, followed by the usual arguments 

 with the tire company. 



Water has the peculiar faculty of pene- 

 trating even the minutest crevices. It is 

 rapidly absorbed by the cotton of the tire 

 fabric. A cut, therefore, is dangerous not 

 simply because it may admit sand or mud, 

 but because it will also permit water to 

 collect. Dampness acts on the fabric of 

 stored tires far more quickly than water on 

 canvas wholly immersed. The fabric is 

 broken down and the casing correspond- 

 ingly weakened. Often tires will burst 

 after having been stored through the 

 winter. 



Much of the expense entailed by blow- 

 outs can be saved by treating a cut as 

 sensibly as you would a hand injured by a 

 little splinter. Pick out the tacks, glass 

 and the nails, just as you would the splinter. 

 Wash out the injury, and then fill it with 



