BROKEN FABRIC.--The fabric of a tire may be ruptured without giving any indications on its outer side. When there is a strong impact force, like a transverse ridge, which will force in the tire, several things occur. First, the body of the tire is flattened out so that it has a bulging cheek on each side; and, second, a strain is produced on the longitudinal fibers. BRUISES.--The result of such a severe bruise is to cause a break, not transversely, or longitudinally, but usually, obliquely, for the following reason. The fabric has one set of its threads running across the tire, and the other set around the perimeter. This arrangement of the fabric usually prevents a straight break in either direction, and the weakest part of the fabric is across the diagonal direction. [Illustration: 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. [Illustration: 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. BLISTERED TIRES.--A blister is a plain case of the rubber being separated from the fabric. At first the injury may be a small cut down to the fabric, which, after being neglected for a time, permits sand to enter, and a grinding takes place, each movement of the parts causing a further separation, and pressure expands the rubber, until, finally, it bulges out and gives an unsightly appearance, as well as starts the tire on its road to destruction. Such defects can be cured, if taken in time, as many compounds are on the market for this purpose. RIM CUTTING.--This is caused by sand or sharp particles being forced in between the tire and edges of the rim, which causes a wearing out at the contact points. Insufficient air is another cause. The tires flatten and are then cut by the metal.