Fig. 17. Illustrating the Strain on Fabric. Fig. 18.
Try the experiment with a handkerchief, as shown in Fig. 17 by stretching it in the direction of the threads; and then look at Fig. 18, in which case the tension is diagonally, or across the corners. This will be sufficient, probably, to suggest to your mind the reason for the break on diagonal lines.
The rubber material is not sufficient to prevent the stretch which the fabric permits, hence the break follows.
Under Inflation.—To permit a wheel to run flat causes a tire to stretch more on the tread than along the clinch line.
Stretched Tires.—A good illustration of this is shown in Fig. 19, where the tread is a succession of irregular wavy surfaces, whereas the sides remain round and full.
Many attribute this to poor or defective tires. The best tire in the market will show symptoms of this kind, if allowed to run when deflated. In such cases the flatness produces a continual pouching out of the sides, which follow the wheel around, and tend to produce a creeping of the fabric.
Fig. 19. Effect of Flat-Tire.
In time the rubber works away, or along on the fabric, until it becomes stretched at the tread, and all the pressure in the tire will not again restore it to the proper condition.